On modern Steam installations this works as you desire. The home button action isn't activated if a valid chord is used.
I've migrated to macOS for the most part so cannot retest. I do use my Steam Controller with my Steam Deck though and haven't noticed any oddness there though, either in Game Mode or BPM in Desktop Mode, so we're probably most likely good. Appreciate you poking this issue!
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Please describe your issue in as much detail as possible:
When I'm in Big Picture Mode, pressing any configured Steam Button chord will cause BPM to return to the home page. The configured action still occurs. When using Steam Button chords, BPM shouldn't be aware of the Steam Button being pressed. It's particularly obnoxious when using chords to adjust the volume for a video you're trying to watch in BPM.
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