I don't know what the laws are around the world, but in terms of what itch is currently doing, here's what I'm seeing It seems wherever you are in the world, if you're not logged in you'll now how to at least declare your age to see https://stawer.itch.io/lucky-paradox or https://stawer.itch.io/. This is what is looks like:
I don't get this if I'm logged in though. Not sure why, maybe they've decided my account is 18+ based on something (like buying games with a credit card perhaps,. It doesn't seem to be to do with purchases, because I don't get prompted for adult games I've not purchased either?)
However, in the UK, there's a slight discrepancy because I get something different when I go to https://stawer.itch.io/, even when logged in, because on https://stawer.itch.io/ I get a message like this:
This seems like a bit of a bug to me, like I'd expect the "Content unavailable" message to also appear on the game page, but it currently just shows the age prompt.
This is all changing so rapidly though, because the "age prompt" feature didn't seem to be live when I originally commented. So I guess that means there could be more changes coming? (They at least need to implement a UK Online Safety Act compliant "strong verification" to allow content to be served in the UK again)