That's not the only place that it's not secure. It says quite literally "not secure" on every page of the forum when you look on the address bar. It has been like that for years. It has the little (i) in a circle instead of the little padlock symbol. And yes, it doesn't use https.
Also, is this site GDPR compliant? I don't recall anything being done at the time at the end of May to work towards this or any notification regarding changes to the privacy policy. Although there isn't any credit card information being exchanged here, there is still plenty of personal data being stored when people sign up, particularly people within the EU, even if the site itself might be based in the US.
Shouldn't this site also have a cookie notice that pops up?