Could dual boot your laptop or run windows in a VM as someone suggested. Onlyoffice was what finally solved the office compatibility problem for me during school. O365 is online anyways and works on Linux...
Replaced gboard with a FOSS keyboard without internet access on your phone? I use and like AnySoftKeyboard.
Are you on stock android or a privacy friendly ROM? That'd be #1 on my list. I use grapheneos on a pixel 8 and would recommend. Whether you have google apps on your phone or not they have access to everything you do on stock android 🤷♂️
Either way I think its important to recognize how much you've already done, and not stress about what you can't change yet. You're already more private than 99% of the general population and you aren't in school forever. I was in the same boat with a windows partition on my laptop for a couple windows only programs for school (online test invigilation can be a bitch for compatibility, windows in a VM generally doesn't work I found), but school ends and that partition is gone now.
TL;DR
You're doing good, don't stress if you have to keep some stuff around for school, give onlyoffice a shot, look into privacy friendly ROMs for your phone.