Where does one seek guidance for a game when there is no forum for said GOG game?

Right here in this forum, of course.

Bit of advice: if you make a thread asking about a particular game, try to put the game's name in the thread title....it makes it easier for those with the answers one seeks to be able to find/reply to it.

I'm curious what game doesn't have a forum at this time, tbh. I'm sure there's a few, thouhg.

google.com

Forget Google, use something like DuckDuckGo or Qwant whenever possible.

You could contact GOG support and kindly ask for them to open up a forum for the game. I wouldn't suspect to receive many answers but you can try once its available. GamezRanker and others already suggested what else you can do to receive help. In the rare case no one's able to help you here go visit Steam and ask there, sometimes the only way to get your answers.