ntfy for push notifications where possible
Signal/Molly (hardened Signal fork)
SimpleX
F-Droid Basic for apks only on f-droid. I highly recommend F-Droid Basic over F-Droid it allows for unattended updates.
As far as installing apps, a good rule of thumb is:
apk direct from dev installed via Obtanium > apk via F-Droid Basic (signed by the dev from their official repository is considered more secure than signed by f-droid) > Aurora > Google Play