I had pretty much the same problem on a ThinkPad T490 after a borked Mint install. It tells the EFI to boot into MOK Manager but doesn't provide it under the path (mmx64.efi).
I don't 100 % remember what I did to fix it but I think I booted into an EFI Shell and wiped boot entries off the NVRAM. Resetting the BIOS should do that, but this may vary by manufacturer.