Reproduction steps:
1. Make sure your Linux device does not have Vulkan support installed (new installation of Linux)
2. Create a new project
3. Go Edit -> Project Settings -> Player
4. Disable auto graphics API for Linux
5. Drag Vulkan to the top of the "Graphics APIs for Linux" list
6. When prompted, click Restart Editor

Expected result: the Editor restarts and since Vulkan device cannot be found, fallbacks to OpenGL, the user is informed either with a pop up or an error in console
Actual result: the Editor restarts and crashes silently. The project will not open anymore, it is impossible to open it without switching the graphics API on another device

Reproducible with: 2021.2.0a16

Note: since I installed drivers I was no longer able to reproduce the issue (therefore test all versions), but it seemed that the behaviour is the same in all versions.