Server Error 403 Forbidden

By internal model I meant within CB Blogs > Parameters > Blog change the Model parameter to Internal. I've retested both Joomla and Internal models as working. So my best guess is the menu item being used as the forms URL is likely what's causing this.

I also noticed that the comment function for posts doesn't work; nothing happens at all.

Ok, then this is absolutely a menu item issue. CB isn't properly reachable. Go through your menu items linking to CB and switch them to Public access 1 by 1 to find which is doing it unless you're comfortable using your browsers developer tools (press F12) to view the network tab to see what URL it's trying to submit to when you comment.

I've now made a video, because I did exactly what you said I should do.

Ok, then this is absolutely a menu item issue. CB isn't properly reachable. Go through your menu items linking to CB and switch them to Public access 1 by 1 to find which is doing it unless you're comfortable using your browsers developer tools (press F12) to view the network tab to see what URL it's trying to submit to when you comment.

Sorry, I'm not that far along yet to understand that.

I'm still a toddler.

You'd need to view the Network tab and you should see a network request in red when trying to comment. Ensure SEO URLs are turned off and then you can see the exact URL and what Itemid it's using in that URL. That Itemid is the Menu ID. You'll then need to find that menu item and adjust its permissions. CB requires there to be a public and published Joomla menu item to profiles and it's specifically to workaround this goofyness as Joomla is very strict about menu access.

If you're still having issues you can PM backend super user login credentials (see link in signature) and I can take a look for you, but it likely won't be until Friday or Monday that I've time to review due to the holidays.

That's it for me. I'm removing Joomla 6 from the server and reinstalling Joomla 5.x.

I wish you all a Merry Christmas.

I don't recommend downgrading over a menu permissions issue. Same problem can happen on Joomla 3, 4, and 5. Usually happens when the menu item we create for you is changed from Public to Registered under the Community Builder menutype.