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I had the same problem. After enabling CSM, I also had to switch it from "Legacy" to "UEFI" mode before Secure Boot became available. Good luck!

This. Did you try freeing up space on your Windows drive, maybe by cleaning out the old Windows update files?

Same here. Yeah, that troubleshooter is a good call. Also, double-check that your antivirus definitions are up to date, as that can sometimes cause false alarms.

This. I had the same problem. For me, it was my old antivirus causing a conflict, and I had to boot into safe mode to remove it.

Agreed, and one more thing – after you clear the keys, you might need to reboot twice before Windows Setup actually recognizes it.

I had the same problem. For me, it was the TPM 2.0 setting that was disabled by default in my BIOS.