Some early game would probably patent "revealing more of the world as you move horizontally/verrically" and we would probably be confined to a single screen for every other game for decade.

Then some other game would patent "using an input source to move a gun's aim/targetting on the screen" and we would never have had any fps. A "first person view" would probably be patented soon too. Leveling up? What a cool concept that I wish more than one game ever used.

At best, companies would all be paying licenses to each other for all of those mechanics - just like it works on hardware today where Samsung (for example) for a long time made a ton of money out of their main competitor's sales. And games would probably be so expensive that a lot of them could even have their own dedicated hardware made specifically for them, without affecting the final price that much.

Modern day Nintendo would surely enjoy that. They could make gimmicky hardware for specific games and simply call it a toy. Games like Guitar Hero would probably only be playable on toy guitars (as some other game would've already patented translating basic inputs into something rhythm related).

In a way I could see some pretty cool games being invented for a while in this parallel reality, with the patent restrictions forcing people to think of new stuff like the hardware restrictions used to do last century - but we would never had Stardew Valley, Minecraft, Rimworld, Factorio, Dwarf Fortress and 99% of the most beloved games out there.