This issue describes the black issue caused by SteamVR sandboxing. Other causes of the black screen issue are also covered on the troubleshooting page though.
Reference workaround for this issue: https://github.com/alvr-org/ALVR/wiki/Linux-Troubleshooting

The black screen issue is caused by a component of SteamVR called vrcompositor running in the Steam Linux Runtime Scout (SLR 1) sandbox, which we can't compile our vulkan layer for. The workaround solves this by partly disabling the sandbox. The workaround is always needed to fix this issue. This is a known issue, please don't report it again.

NOTE: The vulkan layer is needed because SteamVR doesn't expose internal information related to rendering, so the vulkan layer intercepts it for us. An api to solve this called direct mode has been exposed by SteamVR, but it has a bug that makes it unusable currently. Once a fix is shipped we'll use this api, rendering the workaround redundant.