Let me reply to that by listing existing apps listed on http://appl.ist:

- NewPipe > FreeTube, AudioTube

- Podcast app/music app > GNOME Podcasts, GPodder/Lollypop, Elisa

- Maps > PureMaps, GNOME Maps

- AndOTP > Keysmith, GNOME Authenticator, Two-Factor-Keychain, Numberstation

- Signal (and/or Matrix) > Axolotl / various, Nheko feels most complete currently

- Orgzly > Emacs maybe?

- Email > Geary (I still use Evolution though)

- Good browser support > Angelfish, desktop Firefox has been adapted nicely, once Chromiums Wayland supports matures it will also be a viable option (it’s very fast, but has annoying issues with text input currently)