Supraland is the game you want - it fits all your criteria except the most important one: it’s currently Unsupported on SteamDeck. I found reports of people getting it to work but not without some fiddling. It has a sequel, though, which is just as good and which is Verified. The sequel is called Supraland: Six Inches Under.

The first game is an indie gem made mostly by one guy but it is very polished. This sequel was made by a small team. Don’t let the cute graphics throw you - it’s not a kids game. It’s a first-person open world metroidvania (not really a shooter, though there are enemies you’ll be hitting) with gameplay reminiscent of Portal, Zelda, and Metroid. Currently on sale for 40% off ($11.99). About 8-20 hours long.

I helped co-found a guild back when WOW was new - I was the guild webmaster. The guild never really got that big or active, but here it is 20 years later and I still occasionally get credit card offers in the mail for “The Blackrazor Brotherhood.”

Some of my favorite gaming memories are from my time in a guild called The Sylvan Guard on an EverQuest server around 1998 or so. It was a small guild but the last time I saw a question similar to this posted, on Reddit a few years ago, I checked in and so did a former guild-mate I hadn’t spoken with in decades.