Thanks for your help!
As an update on the status of my issue: Yesterday I was able to post the comment I couldn't post before, but I didn't dare to include the link that apparently caused the problem.
Once again, no one notified me that the problem had been resolved—I had to check it myself today. I still don’t have an explanation for why my account was blocked in the first place.
It's a shame that the support email address they usually provide isn't enough to resolve a problem and that you have to post about it on forums and Reddit. And it's a shame that itch.io lacks transparency regarding the reasons for my warning.
But in any case, thank you No Time To Play for your help: you were here lending me a hand when others didn't :)