IEMs are usually much more intimate, so will have less of a soundstage compared to over ears. Soundstage is what is necessary for games to sound expansive and allow you to pinpoint sounds around you.
As long as you don’t buy into gimmicks like 5.1 or 7.1 surround headphones for games you will be fine.
If you are in a true competitive scene, you would use what your sponsors give you anyway and you have no option to change that unless you don’t have sponsors.
If you are streaming or playing heavily at home then open backs such as the Sennheiser 58x are very good cheap over ears for gaming.
If you are playing LAN then I would recommend closed backs so other people don’t interfere with you