Why not Node 20 yet and still npm to install packages

I forked trackit which uses opensass template of wasp. though I successfully ran the project locally, I have 3 questions

1. why can't use 20 yet for wasp? right now I am using 20 lts with all my projects, working fine so far.
2. why can't choose package manager? I usually use pnpm and recently started using bun
3. saw this warning in the wasp docs "Experiencing the 'Bad CPU type in executable' issue on a device with arm64 (Apple Silicon)", didn't use it yet, is it mandatory? my cpu is m3 pro,

Thanks