How can watching be non-doing?

When a loud sound is heard, is this hearing "doing"? When the bright sun is seen, is this seeing "doing"? When a smell is smelt, is this smelling "doing"?

None of the above are "doing". Therefore, why would the automatic natural knowing of internal bodily & mental states be "doing"?

If you want to end suffering (attain Nibbana), you need to develop wisdom which comes from developing the Noble Eight Fold Path. Not by looking at some object.

By developing the Noble Eight Fold Path, you understand the Four Noble Truths.

Just by looking at some object will not bring you any Wisdom. See for yourself if that develops any understanding of the Noble Truth of Suffering? The Origin of Suffering? The Cessation or the Path leading to the cessation of suffering? Sure your mind will be concentrated but without any Wisdom (about the Four Noble Truths). Therefore, such concentration is not the Right Concentration.

In the Great Forty discourse, Buddha clearly shows what Right Concentration is with all the 7 preceding parts (starting with Right View) as their requisite condition. And what is the right view? The understanding of the Four Noble Truths.

Therefore, start with that. Buddha said in the Noble Truth of Suffering that Birth, Aging, Sickness, Death is suffering.

Focus on Birth - contemplate in terms of where one can be born in - hell, animal womb, plane of the departed, human world, divine world & brahma worlds. Contemplate suffering in each of those planes. And ask yourself this being the case, is there any place for me be born and call it a happy destination?

Then look at yourself, aging - compare to how it was when you were a child and how you have aged now. Contemplate on various sickness in the world and how the next moment you can get the same.

Then contemplate on Death. As Buddha said, contemplate on a dead body left out there for days, oozing, eaten by insects and animals, contemplate the disgusting nature of that and think such is the nature of "my" body. I have not escaped this.

Then ask yourself, what is the Origin of such a Form? How did I get this disgusting thing? Then use this below Concentration Discourse and meditate on the arising and passing away phenomena.

https://suttacentral.net/sn22.5/en/bodhi

“And what, bhikkhus, is the origin of form? What is the origin of feeling? What is the origin of perception? What is the origin of volitional formations? What is the origin of consciousness?

“Here, bhikkhus, one seeks delight, one welcomes, one remains holding. And what is it that one seeks delight in, what does one welcome, to what does one remain holding? One seeks delight in form, welcomes it, and remains holding to it. As a consequence of this, delight arises. Delight in form is clinging. With one’s clinging as condition, existence comes to be; with existence as condition, birth; with birth as condition, aging-and-death, sorrow, lamentation, pain, displeasure, and despair come to be. Such is the origin of this whole mass of suffering.

Take your own example and ask do I seek delight in form? Do I eat anything on the table or do I seek something I like? Do I eat and say it's tasty? Do I welcome it? Do I remain holding? Having seen a person do I say he or she is beautiful? Like this just observe by looking at your examples. Then see as a result do I cling to it? The next day also do I want the same thing? Like this contemplate all the way to Birth. This is how I got this mass of suffering.

Now you can contemplate on the passing away phenomena - what is the cessation? See if you did not seek delight in form, did not welcome it, did not remain holding, won't the delight cease? If there's no delight will there be any clinging? Like this contemplate and you see there is a cessation of this form.

Try to understand the Dependent Origination. What it means when the Buddha said "with Existence as a condition, Birth" or because of Craving, Suffering come to be.

This is how you should understand impermanence. By understanding the arising and passing away phenomena of form, feeling, perception, volitional formations and consciousness.

The commonly accepted Vipassana techniques today are all polluted with non-Buddha teachings (mainly due to Commentaries esp. Visuddhimagga and Abhidhammatta Sangaha - both works of non-attainers).

Everything that the Buddha teaches is towards the goal of Nibbana. The whole doctrine is within the Four Noble Truths.

If not for a great Dhamma Teacher I too would be in your boat. Therefore with much compassion I write these details for you to also try contemplating on Dhamma and see the results.

Full meditation I mentioned above can be found here

Case 19 Nansen's "Ordinary Mind Is the Way" 十九　平常是道

南泉、因趙州問、如何是道。 Jõshû asked Nansen, "What is the Way?"

泉云、平常心是道。 "Ordinary mind is the Way," Nansen replied.

州云、還可趣向否。 "Shall I try to seek after it?" Jõshû asked.

泉云、擬向即乖。 "If you try for it, you will become separated from it," responded Nansen.

州云、不擬爭知是道。 "How can I know the Way unless I try for it?" persisted Jõshû.

泉云、道不屬知、不屬不知。 Nansen said, "The Way is not a matter of knowing or not knowing.

知是妄覺、不知是無記。 Knowing is delusion; not knowing is confusion.

若眞達不擬之道、猶如太虚廓然洞豁。 When you have really reached the true Way beyond doubt, you will find it as vast and boundless as outer space.

豈可強是非也。 How can it be talked about on the level of right and wrong?"

州於言下頓悟。 With these words, Jõshû came to a sudden realization.

Mumon's Comment

無門曰、南泉被趙州發問、直得瓦解氷消、分疎不下。 Nansen dissolved and melted away before Jõshû's question, and could not offer a plausible explanation.

趙州縱饒悟去、更參三十年始得。 Even though Jõshû comes to a realization, he must delve into it for another thirty years before he can fully understand it.

Mumon's Verse 頌曰

春有百花秋有月 The spring flowers, the autumn moon;

夏有涼風冬有雪 Summer breezes, winter snow.

若無閑事挂心頭 If useless things do not clutter your mind,

更是人間好時節 You have the best days of your life.

                                *          *          * 

Letting go is ultimately a volitional act, but unlike other acts of volition, it does not give rise to subsequent mental formations. Seeking and trying are dead ends. A good way to put this kind of perception into practice is to avoid the tendency to see meditation as a kind of special state. Any attempts to conjure something "extraordinary" or "concentrated" or even "bare" or "relaxed" is just another act of willful imposition. Just let your mind be ordinary. To paraphrase Suzuki, mindfulness is nothing special.

MN1 The Root of All Things addresses watching for the untrained ordinary person as:

They perceive the seen as the seen. But then they identify with the seen … Why is that? Because they haven’t completely understood it, I say.

In contrast, for the trained mind SN35.96 we have:

...in the seen will be merely the seen;...

The simplicity of "merely the seen" is itself non-doing. Ordinarily we identify with thoughts, latch onto them with greed, aversion or delusion. That latching onto thoughts is the doing to be relinquished. Yet we perceive the latching onto thoughts as "not-doing", hence the seeming paradox.

As we practice, we start noticing the doing, the grasping. And with a measure of watchful restraint we counteract the tendency towards "doing". From AN3.60:

When there is sense restraint, one who has sense restraint has fulfilled a vital condition for ethical conduct. When there is ethical conduct, one who has fulfilled ethical conduct has fulfilled a vital condition for right immersion.

Find the razor's edge between doing and not-doing. Explore that.