Life is Tetris

Do commercial apps work on such an installation? I have seen them get worse, checking for non-rooted, non-developer-mode-enabled, Google Play Store enabled, etc.

More like a vocal minority, I’d guess. Its upto the majority to also be vocal.

Go landfills!

Oh, and. Now I don’t need a separate bookmarks app, a separate notes app, a separate todo list app, syncing mechanisms for them, or a mechanism to search through all of them.

I never liked the fact there is a contacts app which other apps can tap into.

I have started using an org-mode file with entries that have tel: or callto: properties. I lose vCard exportability, but I can use the file as-is instead.

* Open-source

Yes

* Android, Web, and (if necessary) Linux and Windows clients

Emacs on larger devices, Orgzly on Android

* Stores contact info locally (i.e. self-hosted)

Yes

* Stores contact info securely (encrypted)

Unencrypted, but if you don’t allow apps other than syncing apps the permission to access all files, it may not matter as much

* Can store in a cloud location (e.g. Sync, Dropbox)

I just have Syncthing set up to sync those files too

Would the Delta Chat e-mail client or the Monocles Chat XMPP client help? They both support webapps-in-chat (WebXDC), and a calendar is one of the many simple apps already created. https://webxdc.org/