A terse, altered "Hello" is all I say. Sometimes I don't say anything. Most humans would wait a few seconds then prompt with "...Hello?", whereas bots tend to hang up after ~2s silence

That's my experience too. I mostly don't pick up calls from numbers that I don't recognize. On the very rare occasion that I am expecting such a call, I always stay silent after picking up. A real human will without fail start talking after a second or two.

When it is a human scam caller, what I sometimes do is to say "Hello" and then, when they start talking, and I can already guess they are full of shit, I act as if I am not hearing them properly and say "Hello?? Heeellooo? Hello?" Then they hang up lol.

Don’t you guys have phones that screen calls?

Yes, but false negatives fall through. I don't pay for the call screening; maybe a paid version would be more successful.

Mostly ignore unknown numbers, but if I'm expecting a call, I will pick up.

My colleagues regularly get calls from nurseries, daycare, parents at the after school club, friends of their children or their parents and so on.

They can probably ignore international calls, although only probably.

Yep, if the number is not in my comtacts, it goes straight to voicemail.