I’ve played Beat Saber last week on 8KX and RTX2080 and it looked ok. Haven’t changed any settings or software/drivers since then, but replaced GPU with 2080 Super. And now don’t see cubes, just arrows.
Have read on the net, that someone had such a bug and the solution is to set resolution to 1.0 and SS to 100%, but I already have it exactly this way.
Picture not mine, but it looks like this: https://imgur.com/a/qjTrekS
UPDATE: found inside the game settings that resolution multiplier was set to 1.5, changed it to 1.0 and all great again!
UPDATE2: I guess it was Geforce Experience optimization which set resolution to 1.5, so beware.