I'm all for them adding links to the relevant game/series forum on each product's store page, but honestly, unless you already happen to have the game card open, it's no quicker or more direct to open the store page to get to the sub-forum than it is to open the Community page and do a quick search, or do the same with your library, if it's for a title you already own (though I make a point of "favouriting" the sub-forum for pretty much any game I own or have owned...then again, I don't buy stuff that I'll probably never play, so that might not work so well for digital hoarders with massive "collections").

In Safari's "Advanced" preferences a file can be chosen for the "Style sheet". Such a file is just a plain text file, e.g. with a ".txt" ending. I use the ".css" ending for the file name to remind me it has Cascading Style Sheet notation in it.

The following text worked for me when I tested it to hide all the other forum links you mentioned. Just copy paste the line into a plain text file and save, then select it as the style sheet in the web browser preferences. I don't use other web browsers, so you might want to check to see if yours has that option.

#forum_general~*{display:none}

One caveat is that you might want to temporarily unselect the file when browsing websites other than GOG. Otherwise it might also affect other forums, such as if they have an item in the page with the same id, i.e. "forum_general".