My google android phone already does this. I get basically no spam calls at all except very rarely. But I go to the spam tab in the phone app and I see there are dozens that got blocked

That would work well assuming scammers and stuff are actually blocked from spoofing phone numbers

You cannot trust which number which is signalled to the end user.

Most spam calls I get is shown as legit numbers. If I call them back they will go to an innocent and unsuspecting user.

Google is already collecting this information and shows numbers as "probably spam". It is hard to enforce this harder even with collateral damage as you cannot trust the number which is signalled.

Legislation is in this case a good thing which might get the telcos to take this more seriously. This needs to be handled on an operator level. Nothing will happen without legislative incentives.

The world is run on SS7 which has a lot of problems which inertia and lacking incentives makes hard to overcome.

https://en.wikipedia.org/wiki/Signalling_System_No._7

there are some apps that do this, I used to use truecaller, but here in poland orange phone seems to have better data