Various gstreamer libraries have missing dependencies.
ldd /usr/share/steam/compatibilitytools.d/proton-cachyos-slr/files/lib/x86_64-linux-gnu/gstreamer-1.0/libgstadaptivedemux2.so
[...]
libnettle.so.8 => not found
This only affects the SLR-variant. Native-variant uses newer libs
ldd /usr/share/steam/compatibilitytools.d/proton-cachyos-native/files/lib/x86_64-linux-gnu/gstreamer-1.0/libgstadaptivedemux2.so
[...]
libnettle.so.9 => /usr/lib/libnettle.so.9 (0x00007fa8e0197000)