This spring I was applying for jobs so I answered my phone for more unknown numbers than usual. This has lead to a huge increase in spam calls that I receive on a daily basis and Google Phone's spam filter isn't strict enough for my liking (not to mention no longer available since I'm running GrapheneOS). If you're an Android and Tasker user you can take matters into your own hands and set Tasker as your call screen…
I dunno how successful this is, but when I get spam called, I do what I can to reach a person and then say, "Put me on the do not call list, please!" and (possibly) as a result, I really don't get as many of these spam calls as it sounds like folks here are getting.
The problem with your method is that spammers call phones just to see if they pick up. This then confirms an active number that they maintain in their lists. This can be done legally because technically calling and hanging up and never calling again (from the same number) isn't spam. So just don't answer.