Hello. Possible bug.
file: /system/Content/Comment, line 1360:
$container->setLastComment( updatedItem: $this );
I think $this->item() should be here.
Error:
TypeError: IPS\forums\_Forum::setLastComment(): Argument #2 ($updatedItem) must be of type ?IPS\Content\Item, IPS\forums\Topic\Post given, called in /system/Content/Comment.php on line 1360 (0)