[BUG] SteamVR 307 on Vega 56 and Valve Index

[JulianGro]

Describe the bug SteamVR returns error 307 on Vega 56

To Reproduce Steps to reproduce the behavior:

1. Install Vega 56
2. Start SteamVR

Expected behavior SteamVR should work

System Information (please complete the following information):

• Distribution: Ubuntu 18.04 and Debian 10
• SteamVR version: 1.15.1
• Steam client version: 30. September 2020
• Opted into Steam client beta?: No
• Graphics driver version: Mesa 20.2.0 and Mesa 20.0.8 and Mesa 18.3.6
• Gist for SteamVR System Information: https://gist.github.com/JulianGro/e71886c45e399016a9fd892b49360bbb

Additional context On Ubuntu 18.04 the Valve Index shows up as a second screen. On Debian 10 it does not show up as a second screen. Both Ubuntu 18.04 and Debian 10 worked fine with my GTX 1080.

Note: Commenters who are also experiencing this issue are encouraged to include the "System Information" section in their replies.

[JulianGro]

Apparently this only happens when installing on an Nvidia card and then switching to AMD. Installing Debian 10 from scratch worked, even though that Debian installation that I tried before was freshly installed as well, just on an Nvidia card.