Will the Minecraft Nether update also come for cell phones, tablets, etc?

I know there are some Youtubers who are already playing the new update. Is it simply because they can already play it or is it really because of the Java…

The snapshots only come for the Java version. The release when it's done, if nothing goes wrong, on all platforms at the same time.

Ah, OK cool…

Mojang has brought an update twice a year since 1.14. A bigger and a smaller one, that means the 1.17 will probably not be that exciting, although you have to keep in mind that they fixed a lot of bugs as features added at 1.15.