I find blocking numbers on the Galaxy S21 pointless as the caller can still leave a voicemail.
I'm trying to set up a bixby routine where an incoming call from a specific caller will "auto decline call and send a quick message " but this option is greyed out as it 'conflicts with another action '
Yeah, there must be a third-party app for that. In this context, there are loads of third-party apps that deal with call managing, blocking numbers, etc..