I think just doing files and then syncing the files with another solution it's okay.
For example my local apps:
Synthing syncs the files between my computer and phone for
Note taking(just markdown and org files) obsidian on my phone, emacs/vim on my PC.
Todo and reminders: org mode in emacs (desktop) orgzly on mobile.
Password manager: KeePassxc desktop, keepassdx mobile.
Calendar: just sync the ics file.
Photos: just sync files use the default app.
I can continue with this with every app, I don't know why people overcomplicate things
For example my local apps: Synthing syncs the files between my computer and phone for Note taking(just markdown and org files) obsidian on my phone, emacs/vim on my PC. Todo and reminders: org mode in emacs (desktop) orgzly on mobile. Password manager: KeePassxc desktop, keepassdx mobile. Calendar: just sync the ics file. Photos: just sync files use the default app. I can continue with this with every app, I don't know why people overcomplicate things