In Android 9 I found Stop Call Me the only one working. Without excessive ads, simple to configure, unlike other apps this one don’t tell you that a call is blocked (leaving it ringing), but it blocks effectively it.
settings -> gestures
In settings -> gestures (in Italian: gesti) “scorri verso l’alto” : off
True Phone in my opinion is the best phone app: indeed without unnecessary special effects, it offers a remarkable range of features, including choosing the address books.
As an example, you can set davx (/nextcloud) as the main address book, instead of the google one.
Or you can view groups of contacts – which almost no other app does.
Obviously, you can set customized ringtone and sounds. Or easily modify contacts.
But there a lots of interesting features. It is undoubtedly worth trying.