Just ran into this crash myself, fortunately it looks like there’s already a fix.
There’s a changelist in ue5-main branch dated 2022-03-31 named ‘VR PIE: Make sure SetIndependentViewportSize is called on GameThread’ that should fix your issue. Grab a version of ue5-main newer than that and you should be good to go.
https://github.com/EpicGames/UnrealEngine/commit/06aca884cfd143d18e7e1433bd0e566afe320b71