You typically will not get an official answer here. This is the community message boards. Not tech support. And the moderators can only cite faqs and experience to you. Also, you asked other members in your text how well that advertisement worked and not for an "official" stance on links to external sites. (That's maybe lost in translation. You probably meant allowed with valid.)
I am not aware of any bans on promoting any of your socials. Including creator support sites. Itch is as liberal as it can get with that.
Some common sense should apply of course. Creating a sfw page that links to adults only content for example. Or linking to sites that host malicious advertisements and such. It should be obvious that that's a bad idea.
Also, https://itch.io/docs/creators/quality-guidelines#avoid-only-uploading-keys-or-li...