Trying to find causes of everything

It's correct that these things should not be contemplated due to their ability to destabilize the mind, making it less suitable for meditation practice. Thinking about such topics is useless from a Buddhist point of view.

Just be mindful of the habit and the thoughts when they arise. With time and practice they will subside.

In many ways, it is exactly our inquisitive nature which has been carving away our ignorance of reality for millennia by asking questions which were deemed unanswerable or were patched up with apologetics like "God did it, and we cannot understand it".

The Buddha himself set out to find the answer to such questions, and to be critical of what is deemed answerable, answered, or impossible to answer. The Kalama Sutra states:

• Do not go upon what has been acquired by repeated hearing (anussava),
• nor upon tradition (paramparā),
• nor upon rumor (itikirā),
• nor upon what is in a scripture (piṭaka-sampadāna)
• nor upon surmise (takka-hetu),
• nor upon an axiom (naya-hetu),
• nor upon specious reasoning (ākāra-parivitakka),
• nor upon a bias towards a notion that has been pondered over (diṭṭhi-nijjhān-akkh-antiyā),
• nor upon another's seeming ability (bhabba-rūpatāya),
• nor upon the consideration, The monk is our teacher (samaṇo no garū)
• Kalamas, when you yourselves know: "These things are good; these things are not blamable; these things are praised by the wise; undertaken and observed, these things lead to benefit and happiness," enter on and abide in them.'

In the Zen tradition students are still given Koan (questions that cannot be answered logically, only experienced). The rational mind being stuck can be a powerful tool in meditation. That's very different from saying the rational mind is somehow not beneficial.

Also, who can judge which questions are answerable and which are not for another person - or even for himself? Imagine the Buddha, Darwin or Einstein having this attitude towards inquiry.

And finally, as to your question on what (not) to forget, to think, to ask: it is impossible to force these things, that's not how the mind works. It I write "do not think of a white rabbit", you cannot stop that thought from arising anyway. Meditation is a tool to learn to see that thought arising and dissipating in the mind without self-judging or attachment to oneself or the thoughts that arise.

If you investigate the reasons for thinking distracting thoughts you will find that it's based on unskillful motivations.

"Five things should be reflected on from time to time, by the bhikkhu who is intent on the higher consciousness. What five?

When evil unskillful thoughts connected with desire, hate, and delusion arise in a bhikkhu through reflection on an adventitious object, he should, (in order to get rid of that), reflect on a different object which is connected with skill. Then the evil unskillful thoughts are eliminated; they disappear. By their elimination, the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation).

Like an experienced carpenter or carpenter's apprentice, striking hard at, pushing out, and getting rid of a coarse peg with a fine one, should the bhikkhu in order to get rid of the adventitious object, reflect on a different object which is connected with skill. Then the evil unskillful thoughts connected with desire, hate and delusion are eliminated; they disappear. By their elimination the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation).

If the evil unskillful thoughts continue to arise in a bhikkhu, who in order to get rid of an adventitious object reflects on a different object which is connected with skill, he should ponder on the disadvantages of unskillful thoughts thus: Truly these thoughts of mine are unskillful, blameworthy, and productive of misery. Then the evil unskillful thoughts are eliminated; they disappear. By their elimination, the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation).

Like a well-dressed young man or woman who feels horrified, humiliated and disgusted because of the carcass of a snake, dog, or human that is hung round his or her neck, should the bhikkhu in whom unskillful thoughts continue to arise in spite of his reflection on the object which is connected with skill, ponder on the disadvantages of unskillful thoughts thus: Truly, these thoughts of mine are unskillful, blameworthy, and productive of misery. Then the evil, unskillful thoughts are eliminated; they disappear. By their elimination, the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation).

If evil, unskillful thoughts continue to arise in a bhikkhu who ponders on their disadvantageousness, he should in regard to them, endeavor to be without attention and reflection. Then the evil unskillful thoughts are eliminated; they disappear. By their elimination, the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation).

Like a keen-eyed man shutting his eyes and looking away from some direction in order to avoid seeing visible objects come within sight, should the bhikkhu in whom evil, unskillful thoughts continue to arise in spite of his pondering on their disadvantageousness, endeavor to be without attention and reflection as regards them. Then the evil, unskillful thoughts are eliminated; they disappear. By their elimination, the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation).

If evil, unskillful thoughts continue to arise in a bhikkhu in spite of his endeavor to be without attention and reflection as regards evil, unskillful thoughts, he should reflect on the removal of the (thought) source of those unskillful thoughts. Then the evil, unskillful thoughts are eliminated; they disappear. By their elimination, the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation).

Just as a man finding no reason for walking fast, walks slowly; finding no reason for walking slowly, stands; finding no reason for standing, sits down; finding no reason for sitting down, lies down, and thus getting rid of a posture rather uncalm resorts to a restful posture, just so should the bhikkhu in whom evil, unskillful thoughts arise, in spite of his endeavor to be without attention and reflection regarding them, reflect on the removal of the (thought) source of those unskillful thoughts. Then the evil, unskillful thoughts are eliminated; they disappear. By their elimination, the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation).

If evil, unskillful thoughts continue to arise in a bhikkhu in spite of his reflection on the removal of a source of unskillful thoughts, he should with clenched teeth and the tongue pressing on the palate, restrain, subdue and beat down the (evil) mind by the (good) mind. Then the evil, unskillful thoughts connected with desire, hate and delusion are eliminated; they disappear. By their elimination, the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation).

Like a strong man holding a weaker man by the head or shoulders and restraining, subduing and beating him down, should the bhikkhu in whom evil, unskillful thoughts continue to arise in spite of his reflection on the source of unskillful thoughts, restrain, subdue and beat down the (evil) mind by the (good) mind, with clenched teeth and the tongue pressing on the palate. Then the evil, unskillful thoughts connected with desire, hate and delusion are eliminated; they disappear. By their elimination, the mind stands firm, settles down, becomes unified and concentrated, just within (his subject of meditation). https://www.accesstoinsight.org/tipitaka/mn/mn.020.soma.html

The Dalai Lama, in The Universe in a Single Atom

Despite the scriptural tradition of the Buddha's refusal to engage on this level of metaphysical discourse [such as asking whether the self and the universe have a beginning], Buddhism as a philosophical system in ancient India, developed a long history of delving deeply into these fundamental and perrenial questions about our existence and the world we live in. The Tibetan tradition has inherited this philosophical legacy.

My assessment is that in Tibetan Buddhism at least, rationality is part of the spiritual path. Perhaps you can read some of the dialogues between the Dalai Lama and western scientists (Mind and Life publications).

There is a difference between trying to find the answers to things you're unlikely to find answers to and seeking answers to questions that may have obtainable answers. For example, trying to imagine the beginning of life just for the sake of wanting to know and coming up with many theories is not likely to turn up answers. Getting a degree and studying the origins of life, designing experiments and so on, well, the academic world might drive you mad, but the work of doing research is both likely to be satisfying and might even gain answers.

So no, you don't have to give up seeking answers to all questions. Maybe take the Buddha's advice and simply notice what effect certain types of questions have on your own peace of mind, and on those around you.