If youre coming on Nixos, I have a lot of resources in the bookmarks section here: https://codeberg.org/BlastboomStrice/LinuxPlan/src/branch/main/LinuxPlan.md#nixos-bookmarks
(This was a guide I made for myself in the span of ~4months to transition to linux and I still update it some times.)
This is a good comparison of messengers here:
https://eylenburg.github.io/im_comparison.htm
Btw, an imprtant aspect of privacy is how metadata are handled/leaked. Signal trues to minimize metadata leak to near zero (there are some other messengers that do that, like simplex)