Only requirement is it had to be released in 2021. Remasters are OK I guess, like Mass Effect.
This is a good article to refresh our memories of which games actually came out in 2021
https://www.pcgamer.com/new-games-2021/It's a bit shocking to me, but I started to think of what my answer would be, then as I thought of each title I was like, that didn't come out this year. Over and over again it turns out nearly all of the games I played this year were released before this year. I won't list them all, but I played a lot of Fallout 4 and New Vegas, that covered nearly three months of my gaming. A lot of Borderlands (BL2, BL3, TPS). Some GTA 5 and RDR 2, Elite Dangerous and many more.
Of all the games that were actually released in 2021 I saw just three I played. So I guess these will have to be my nominations for 2021 game of the year, more by default than acclaim.
F1 2021
Disco Elysium (Final Cut)
Sniper Ghost Warrior Contracts 2
That's it! Hard to believe. I would have bought Hitman 3 if it had come out on Steam. It surprises me that the list is so short, but maybe it shouldn't. My M.O. is to wait for sales, wait for patches and DLC, for Game of the Year editions. It's very common to wait a year or two and then buy it. Fallout 4 and Rome 2 were two games I bought this year, years after release, and crucially in my view, after they were made whole by patches and DLC. Doesn't hurt to save some money either. Fallout 4 was ten bucks and I got 350 hours out of it so far. But still, there's usually a must-have new release that I can't resist. But not in 2021 I guess.
So yeah, I'll nominate F1 2021 as my game of the year! Haha, but that's only because my list is so short. What a year, eh?