Steam is over run with spam, scam and other link sharing. Users have links on profile name, bio, comments, guides, screenshots and everything else where user content is allowed.
Valve is trying to fix the problem with their link filter which can block out dangerous links and warn about suspicious links, sometimes even about safe links. Only very few trusted links can opened directly without ending up on the warning page before you may open the link.
But it also can cause a lot of headache when they block too much.
For example now for the past week and a half all .pro domains have been blocked across the whole Steam platform. First week or so it was blocked everywhere. Now it’s only blocked in Steam messages, Steam profile page bios (not including group bios) and profile comments. Which means I cannot have the link to my (this) website on my Steam profile bio text and I cannot link anyone to any page on my website via Steam message.
This is not the first time they have blocked a whole top-level domain. Previously nearly all .ru domains were filtered in November-December 2016 because of a promotion and/or discount on .ru domains leading to massive amount of spam, scam etc in Steam platform.
I have not personally seen any .pro domain scamming or spamming in Steam but still, I have to suffer from it too.
At the moment I am “bypassing” the block by using my another domain on .net tld to redirect here in my bio and profile comments.