It's supposed to be treated more like a modern-day mute feature than a true "block" feature, but it doesn't even do that well.
If I mute someone anywhere else, the whole point is that I'm not shown their comments or posts without actively seeking them out. If I "mute" someone on itch, it doesn't even stop them from showing up in my main notifications feed. I haven't seen any sort of blocking or muting feature on any other site work that way, save for maybe Twitter after already starting its descent into a Nazi-run cesspool.