Shouldn't we take Lord Buddha's word above the all others?

What are you saying?

The teachings must be interpreted because they are very subtle, deep and difficult to understand even if one is an arahant. Also the Buddha taught to many different students, gods and audiences. This causes much need for interpretation.

But as i have learned, Lord Buddha's understanding is above any other,even above an arahant.

Maybe. But I haven't met him, and I'm inclined to believe none of us have. So I can't really put his word (which word? where?) above any other even if I wanted to.

Dhamma/Dharma itself is timeless and therefore does not need modifications or updates.

There are proposals for clarifications and emphasis -- people just disagree with them and each other.

So what is the need of the term "Modern practice / Modern Buddhism"?

Times change, methods change, pedagogy changes. The subject at hand might still be the same, what one ends up learning might still be the same, but the ways of teaching them always change with cultural and geographical developments.

Shouldn't we take Lord Buddha's word above the rest and use any other resource later on for further clarification if there is such a need?

Some people take mainly the surtas (e.g. pali) to be his words, others take mainly their master's teachings as his word, and so on. Could the sutras contain misrepresentation of his words? Could a master misrepresent him? If so, what is the Buddha's word?

Why there is a trend of drifting away from original teachings, does the followers now believe that Lord Buddha's words are outdated?

What original teachings? Hundreds of years after his death, different regions across asia ended up developing different canons. There are remarkable overlappings, but there are also some disagreements. And within agreements in words, there are disagreements in interpretation. What is the original interpretation?

Some literal teachings could be deemed outdated, yes. For example, westerns have a very hard time sitting cross-legged. Should sitting in that position be paramount for buddhist practice just because a text have the Buddha mentioning that one sits cross-legged when practicing meditation?

Other teachings could be seen as figurative and unfitting for a "modern mind": rebirth is a favorite one here.

There's always a trend of drifting away of anything. One (buddhist) answer is because that's what a wordling mind does: it drifts away.

But in a gist, those who bring something new (or modern) in contrast to a set of texts are either doing because:

1. they regard it as compatible and the same with what the texts teach
2. they challenge the authenticity of the text

Let me try and address this question at the level it was asked on.

Buddha himself said we should go to elders with questions about Dharma. In every generation there are students who learn from elders, and then grow old and become elders themselves. This is how the "modern masters" come to be. Where did you think they came from?

Modern masters are the translators and the explainers who were students like you and me, who had teachers, and those teachers themselves had teachers - all the way back to the Buddha. What's wrong with this?

You don't think commentaries and detailed explanations are useless, do you? Guess what, some of them, like Visuddhimagga, were written 900 years after Buddha's parinirvana! Let's throw away commentaries then? Or do you think written commentaries are better than verbal commentaries? But back in the Buddha's times elders did not write down their explanations...

Or are you saying the role of the teacher is to just repeat exact words of Buddha from suttas, without trying to summarize the points, explain the meaning, and show how it applies in practice? Especially if the elder is an arahant, don't you think they can explain some details that Buddha explained but that were not captured in suttas?

You see that life has changed, don't you? Buddha-Dharma goes to societies and cultures that don't live like ancient Indians at all. People work in offices. There is internet. There is neuroscience. There is genetics and memetics. There is medicine. There are drugs. There is astronomy and space travel. There is psychology and psychiatry. Also, the social discourse has developed many subtleties that were not there. There are many more attachments these days and many more ways to get confused with logic and knowledge.

Despite these changes in life style, knowledge, and culture, the teaching is not drifting anywhere. It's not like in the last 1000 years it has drifted further than in the first 1000 years or even the first 200 years. The teaching is always the same, it is only that every generation of students when they become teachers explain it on the examples that you can see in your actual life.

In short, there is no "modernized" Buddhism vs. "original" Buddhism - there are just people who apply Buddhism in their lives today, and the stories they can tell from their experience. If you deny the real-life experience of the modern elders, then you should be consistent and deny everything except suttas. And maybe we should go to Mahasi Sayadaw, Goenka, Ajahn Chah, Thanissaro Bhikkhu, ven. Yuttadhammo, Dalai Lama etc. - and tell them we don't need them because they explain things in modern ways? I don't think Buddha would approve of that.

I have seen many answers to questions referring teachings of modern teacher in this SE.

But as I have learned

Lord Buddha's understanding is above any other,even above an arahant.

I also believe the same. There are 3 things. pariyatti, patipatti and pativedha (‘theory’, ‘praxis’ and ‘insight’). Generally faith should be based on insight. When you look at the Suttas and do what is there your experience to a varying degree some insight which re reinforces your faith. One should give fair trial and experimentation to the techniques in the Suttas to develop this faith. Many later developments may not give the same results or insights or may hit a wall at some point. The appeal for later developments are that they do give some result or the other which can be mistaken. The Suttas will have the most holistic approach. Nevertheless, there are pitfalls and tips and tricks which are not there in the Suttas. Insights into there are gained through teaching numerous students and their experience. These are also invaluable as long as they are not tangential or contrary to the Tipitaka.

Also it is the lineage of teachers who preserve the teaching and practice. There might be some differences. These are best studies to see what is the best interpretation that works for your and help you further in your practice.

Dhamma/Dharma itself is timeless and therefore does not need modifications or updates.

So what is the need of the term "Modern practice / Modern Buddhism"?

Shouldn't we take Lord Buddha's word above the rest and use any other resource later on for further clarification if there is such a need?

Why there is a trend of drifting away from original teachings, does the followers now believe that Lord Buddha's words are outdated?

I believe this is no needed to modernise Buddhism. Ani Sutta makes references to how the Dhamma may end where disciples tend to study the later works than the original teaching. Also see The Dharma-ending Age which highlights how the Dhamma may end.

It is correct, that the Dhamma is both universal and timeless.

The Dhamma is described as being an ancient path, that fully enlightened Buddhas discover by themselves and then teach it to other beings.

The words from a fully enlightened Buddha need not to be renewed or changed.

One needs only to practice insight meditation to find out if these words are true or not.

So there is no need for renewal of the Dhamma. The Dhamma is complete as it is. The Dhamma does not change.

Don't worry about the shifting away from the Dhamma. That is bound to happen. That is why there will arrive a future Buddha. The next fully enlightened Buddha to be, is Maitreya, whom arrives when the Dhamma has been completely forgotten. That is just the nature of a world system.