FEX is to allow running x86 programs on ARM, but they’re only targeting the Steam Frame (SteamOS/Arch Linux) right now.
That VR headset uses a processor similar to phones, but they have not announced anything about moving to using these tools to allow you to play Windows games on Android
There are several moving pieces, so I understand the confusion
ricecake@sh.itjust.works 15 hours ago
This image seems to explain it.
Image
Proton is the windows compatibility layer. Lepton is the android compatibility layer. FEX translates x86 (most desktop computers) applications to run on ARM (most mobile devices).