A game can be snapped even if it requires 32-bit libraries, as they can be bundled inside the snap. If built on 18.04, that archive can be used to source 32-bit libraries from.
However. Nobody is going to go through all the games in Steam, GOG and Itch.io (and whatever sources) and package them all up as snaps or flatpaks. Game developers have a well known process of putting out a game, and moving on to the next one. They often don’t re-visit a game to rebuild / patch / update it unless it’s financially profitable to do so. For example repackaging an old title for a new system such as the Nintendo Switch. As a result there is an expectation that games continue to work forever, without needing to be rebuild / repackaged.
So. With that in mind, I did some testing over lunch today. I took a few games from GOG and tested them on a 64-bit only system - eoan with 32-bit support removed. You can find the results at the thread below. It’s not pretty.