If you're playing on PC. I had the same issue that BF6 wasn't letting me record anything.
I fixed the issue by uninstalling BF6 beta from my system. If you're sitting thinking, "I've already uninstalled it." Double check. I went into, Start > Settings > Apps > Installed Apps, find it under BF6 Beta or whatever name it has and uninstall it from there.
I also uninstalled the NVIDIA Control Panel and NVIDA app for good measure. Restarted my PC, reinstalled the NVIDIA software with the latest version straight from their website. Used the custom option and reinstalled it completely fresh, it removed all previous settings.
Restarted again. Loaded back into BF6 with the Instant Replay on and it worked. Bit of a ball ache but hey ho.
Maybe the same thing for Xbox, I don't know? Try uninstalling the Beta if you haven't already. Maybe remove all saved settings from the drive/cloud for it as well so there's no trace left.
Best of luck all. See you on the Battlefield.
