Because, you won’t have to guess where to download the app. And you can get a completely FOSS version. And if not using google services, unified Push can help you with notifications.

This is c/opensource

Logseq is a good alternative.

You should consider using Molly, a fork of Signal with Unified Push.

Making a work profile using Insular or something? Or maybe create a different user?

I believe you can still access internet-banking, without the need for an app?

Maybe, setup MicroG. If the your bank app just redirects you to google play store app, I think Aurora Store might be able to fool it, considering you disable or remove GPlay using adb or something.

I got Nextcloud on Hetzner. Technically, Hetzner can see the contacts stored on their servers, but I trust them enough, and everything is open source.

You can also self-host Nextcloud.

Who told you to not use Signal, and what reasons did they give? I’m very curious.