In theory you could change the steam command line fpr each game and have them launch in bubblewrap. Though I'm not sure how well that would play with graphics drivers. It might be friendly with AMD, but my experience is that NVIDIA is a pain to have play nice with containers.

I sandbox Steam itself for simplicity. My experience with Nvidia and Wayland has been good. I simply exposed /dev/nvidia*, a few networking-related files in /etc and system binaries like /usr.