You are describing the same thing I am experiencing, however constantly restarting the sim and/or entering and exiting VR mode a few times sometimes results in the sim running with the expected level of performance. Something in the recent update has caused this.
I’ve made multiple posts on this and have seen multiple posts from other experiencing the same thing. It’s the sim, it’s not you.
Reporting it via zendesk just sets in motion the usual advice on updating drivers etc.
Personally I’ve given up and stopped the gamepass subscription until it’s sorted.