It's way worse on RISC-V. There are maybe 5 x86 or ARM variants to care about at any given time, even if you want to hyper-optimize your code. RISC-V has a soup of literally 100s of extensions with non-uniform use and support.

What are you imagining? If this is desktop then most of the extensions are going to be standard.

The only reason they're optional is because I'm using the same instruction set on my Pico, so no it doesn't have floating point, and I believe it has integer divide but I wouldn't be surprised if it didn't.

And the extensions are in groups, a good chunk of which are compressed instructions, which unless you're writing assembly, you don't need to worry about.

In fact most of this you don't need to worry about unless youre writing assembly.