Some of those languages (especially python & php) utilise C based modules or packaged external binaries. Both of which have to be available / compatible with ARM.

When you run pip or composer on Amd64 they often pull these down and you don't notice, but if you try on arm you discover quickly that some packages don't support ARM. Sometimes there is a slower fallback option, but often there is none.

As far as I can tell, yes. Docker images compiled for arm64 work fine on the Macs with M1 chips without rebuilding. And as another commenter said, you can compile a binary on a Raspberry Pi 4 and move it to a EC2 graviton instance and it just works.

it will probably be a similar situation to x86, with various vendors implementing various instructions in some processors that won't be supported by all. I guess the difference is that there may be many more variants than in x86, but performance-critical code can always use runtime dispatch mechanisms to adapt.

> can you compile for ARM and move the binary around as easily as you can for x86?

Yes.