The latest release of snapd, the engine that installs, manages, and configures snap apps, includes a couple of changes that improve the performance of the Steam snap specifically.
Snapd 2.65 sees the removal of “all AppArmor and seccomp restrictions to improve user experience”.
This doesn’t mean the Steam runs un-sandboxed, rather the Steam snap is more in control of its own containers (Steam is really more of a framework than app, with multiple components, parts, and so on).
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Anecdotally, the latest Steam snap release paired with snapd 2.65 is also reported to open faster than before, with launch times on-par with those of the DEB version. They’re also reported to be a couple seconds faster1 than the Steam Flatpak.
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Not strictly Steam related, but perhaps relevant from a gaming POV, snapd 2.65 also ships with improved snap-confine and OpenGL interface compatibility with NVIDIA drivers.
It definitely is much better than before and has some niceties over the flatpak. Games are added to your app launcher, no need to fuss with permissions if your games are stored on a secondary drive, and you can optionally tell it to use more up to date mesa versions.
Though personally I am sticking to the flatpak. I like that it has less filesystem access by default. I also encountered some irregularities with the snap when using Black Myth: Wukong’s benchmarking tool: https://github.com/canonical/steam-snap/issues/403.