As you can see in the screenshot, all it says after pressing the post button is "Please wait. Processing...". It never ever proceeds past this point, no matter what web browser I use. I've tried all the browsers I use: LibreWolf, Mullvad, Floorp, Firefox and Brave. None of them let me post on the community forums. I tried this 2 or 3 days ago too; same problem. Has anyone else run into this issue?
This looks like an error on GOG's end. Did you try to delete all cookies and cache (for GOG) and try to login again? Ctrl+F5 should do the trick. I would suspect Librewolf's strict security but since it happens on others as well, it doesn't seem like the issue here.