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