Is there a Game-specific forum section like Steam's "Discussions" or is that solely at the creator's discretion?

On a similar note, is there a way to give feedback/ask questions to creators? The rules to post here say "if you need to contact a developer directly consult their game's page." but the option is not always there.

If a game page doesn't have comments or a forum enabled, check your support page for a contact e-mail, or else the creator's website / social media. When not of these options are present, there's probably a reason for it.