How did the Arab tribes seemingly appear out of nowhere & then defeat the Persian Empire and the Roman Empire, then conquer India and Indonesia? Did they have advanced weapons like rifles?

 Lets start from the easiest question

Nope. They did not have any advanced weapons superior to that of their enemies. The advanced logistics based on the fact they were herders used to lots of camels and horses is the best edge they could have. But I’m not really sure they had

The actual answer for your question is two-fold

First of all - Arabs had been around since very long time. They only were not united and they spent most of the time fighting among themselves. That’s BTW why they had polygamy - men were killing themselves in fights so often. Muhammed united those fierce tribesmen… thus it was the matter of time when they will seek enemy outside the Arab Peninsula

The second part of the answer is what have happened before

Justinianic plague have happened.

The plague spared however remote and sparsely populated regions

This same plague enabled Anglo-Saxon conquest of Britain and the expansion of Slavs in Eastern and Central Europe. In the new world those who had been spared by the plague became more numerous than those who had survived it…

There were also other causes: several decades of Sassanid-Byzantine wars, And religious conflicts both within Eastern Roman and Sassanid empire.

[Battle of Niniveh between Sassanians and Romans. Painted in 16th century by Italians so not exactly historically accurate. But it looks cool so I put it here. Also it is less misleading than some Middle -Estern stuf orm 16th century because you see it isn’t historically accurate at very first glance]

The Middle east was ripe to reap!

And BTW it wasn’t the first time when some Semite nomads conquered it.

Before Arabs you had Arameans. And before them Amorites… It was a cyclical thing there… kind of.

And about India… Well India also had been being conquered by outsiders cyclically.

And Arabs actually did not conquer that much of India. Much more had been conquered by Mughals centuries later.

And in the case of Indonesia - Indonesia was ruled by Hindus (Majpahits) as late as 16th century)

So it became Muslim way later than Middle East

And it seems like it was... Kind of grassroots. And kind of peaceful. The Muslims married into influential Indonesian families and converted many locals, which lead to gradual Islamization of Indonesia without one clear Muslim conquest…