Bootrec / fixboot access denied c: partition 464 gb in size?

Unfortunately, my laptop with Windows 10 no longer boots up completely, which is why I tried to repair the whole thing with bootrec / fixboot. Unfortunately access denied appears to me. I wanted to fix the whole thing now with the classic steps, but I don't know which partition to use because my C: partition is 464 GB (that's the size of my entire hard drive, since the Windows folder was always on the C: partition) . I don't want to format them because then all the data would be gone. Two more partitions are shown to me which are possible, namely one with 450MB and one with 979MB when the name is only in the 450 MB partition restoring… So very likely restore or something. Can anyone help me find the right partition?

Can it be the computer boots in EFI mode? Then it can't work that way. The Bootrec.exe command repairs defective MBR bootloaders. In EFI mode, however, no MBR bootloader is required. Therefore the procedure is a little different in this case and so are the commands.

https://www.heise.de/...68553.html

I think the point "Repair of the boot manager: GPT" will help you here.

Thank you!

Unfortunately did not help