gnuzilla does not publish to f-droid - upstream projects generally do not publish prepared packages of that sort - if you find a problem with any pre-packaged binary icecat, or youd like the package upgraded in that repo, you would need to contact the person who publishes the package
i dont know about the f-droid repo specifically; but normally, the package itself would tell you who the packager was, with contact information and how file bug reports but WRT gitlab.com specifically, it is not likely that upgrading icecat would change the behavior - the reason why you can not log in is documented in BR #47276 "Stuck at Cloudflare 'browser checks'" - that includes patches to make it work (and other websites guarded by cloudflare); but the patches have not yet been accepted into icecat https://debbugs.gnu.org/cgi/bugreport.cgi?bug=47276
