In the menu of CS:GO R8_SRGB textures are uploaded and read back, and since R8_SRGB can't be read back on GLES, because it is not a rendertarget format and glGetTexImage and siblings don't exists, we can't default to enabling reading back this format. This leads to an emulation of the glGetTexImage calls issued by CS:GO, and this slows down the menus a lot (below 1 fps on Intel XE hosts).
So add this driconf tweak and enable it for CS:GO to work around the issue. It can be done safely, because in this case we actually can use the data that is stored on the host in the backing IOV.
This tweak lets the CS:GO menu run at around 60 FPS when run with virgl on a Intel XE host.