technically, this is still possible. but there are too many things that can go wrong. you - or anyone who agrees to help you - should be prepared for a lot of work.
in any case, android already allows calls to be routed to voicemail; you don't need a bespoke app. you set up a kind of "whitelist" in the device's do not disturb
settings which allows certain calls to go through as normal. people not in the list are sent to voicemail. android doesn't want you handling phone calls.
I figured with all the Android OS changes it would be a pain, but an app for one person/OS might be doable. It was under notifications and had contacts only. Thanks for the tip. Guess I will get back on something I wrote in B4A years ago and have some fun now.
I went into settings, notifications I believe and found mine. It had messages, what apps can run, etc. Will see if I have a calls like you have. But the junk/spam is always a call or text, and rare a whats app.