Looks like Proton with Intel XeSS is set for some improvements, with Intel submitting code directly to Valve.
https://www.gamingonlinux.com/2026/10/intel-submits-code-to-proton-to-improve-xess-to-use-the-fast-upscaler-xmx/
GamingOnLinuxIntel submits code to Proton to improve XeSS to use the fast upscaler XMXLooks like Proton with Intel XeSS is set for some improvements, with Intel submitting code directly to Valve.