I use tuta mail and tuta calendar for mail and calendar, Vivaldi as browser on laptop, and Firefox on android. Bitwarden as password manager and bitwarden auth as 2fa. Use obsidian for notes and appstore is aurora store and droidify, I use archlinux. And for "cloud" storage, actually a backup I use This USB drive not cloud Buf works for me. Still kinda dependent on proprietary messaging platforms, but I have 1 friend on signal. Also I am trying to replace YouTube with fmhy.net not exactly YouTube alternative, but has so many resources for free to study, educate myself, or just watch something out of amusement.
Zen instead of Vivaldi, KeePass instead of Bitwarden
Aurora is just a frontend for Google play afaik so i don't know if it even counts. your best bet is fdroid obviously but in terms of apps available it's lackluster af and the UI looks like android gingerbread or something.
obsidian's cool but it's not keep-like at all. don't know what would be a good alternative off the top of my head but i bet there are tons.
I recommend Joplin. Doesn't have Obsidian's fancy UI or add-ons, but the core functionality is the same. Should be great for the vast majority of users.
They recently overhauled it and it looks mostly modern. Still not perfect, but definitely a lot better than it used to be. There are also third-party front ends. Can't really say anything about them as I haven't used any.
never knew about the frontends; thanks