Lista Robinson works great in Spain though, enroll there and enjoy the silence :) May take a month or two to really kick in, and if you've already enrolled but it's not working, check that the details are 100% correct. Worked both for me, my wife and tons of friends, although it takes time before it works.

At least a strategy to ignore unknown international numbers has much less collateral damage if any.

All emergencies from unknown numbers that I can thank of will be from local numbers.

I personally answer all phone calls but I have very little of those spam calls (on average once a month perhaps?) And I have learned to just rudely stop the call without saying "sorry, I'm not interested".