Update 32.20200618.0 breaks Steam Proton games

With the recent 32.20200618.0 Silverblue update, Proton games no longer work. When starting a Proton (5.0-9) game you get a black screen. It happens with newer games like The Witcher 3, Doom (2016).
I have a Radeon graphics card.
I guess the problem is in the mesa drivers included in the update.
I have reverted to 32.20200616.0 and all games work as expected.

Is anyone able to play Steam games which use Vulkan with Proton?
I have found a mesa issue which points to the Freedesktop runtime.