This underscores a major issue with commercial software like Steam and games obtained therein. You cannot trust that software not to maliciously scan your device for secrets such as crypto wallets or other information. Ideally, you want to run apps like Steam, Discord, Zoom and whatever else does not come from a trusted distribution repo as a separate user. This is not always convenient however, and the compromise I adopted on my gaming PC is to bubblewrap Steam. Do not mount things like /home and devices games should not be using in the sandbox.

Agreed. I’ve always disliked having anything to do with gaming on my primary OS, always choosing to compartmentalize that stuff away from anything sensitive. The only exception is DRM free standalone games like Factorio, which has pretty safe mods compared to something like Minecraft.

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.

This is what my Steam Deck is for. There's no gap like air gap.

flatpak is the most convenient way to securely run steam on linux

Android solves this problem by making it impossible for an app to access the storage of another app. No matter how much the Steam app wants to see your crypto wallet's key it is not possible (assuming no Linux exploit).