I had this issue. In my case, I had imported my Desk and Sofa into the Oculus Quest 2 environment using the experimental settings. I had to delete them, then the floor went back to normal. ( It was I agree, soooo infuriating !!)
On further investigation, you also need to be stood up when you are given the instruction panel on how to play darts and your (1/3) eg. win / lose ratio. If you are sat down when you click start, you will not be able to reach the darts.
This is a BUG, developers ????