I replaced my rather old motherboard with a not-quite-so-old one, reinstalled EOS, and am now receiving these error messages during the boot process:
What does this mean, and how should I deal with it?
The first one is not an error, it simply tells the user that SGX extensions of the cpu are disabled or unsupported. If updating the bios/UEFI does not fix this there is nothing you can do about that. This is not a problem so don’t worry.
The others i have never seen before
Here is some info https://softhints.com/linux-mint-integrity-problem-loading-x-509-certificate-65-before-login/
Did you disable secure boot in bios/uefi?
Or it might that your iso image used for the usb creation is corrupt? Did you checked the iso?
Yes, I think those 2 integrity messages might have something to do with Secure Boot, see here for another reference:
I fount this topic:
It looks like this is a problem that occurs specifically with Gigabyte boards. I have one of those.
Had the same problem with my Gygabyte board concerning the X.509-22 error.
Those certificates are only needed if you have secure boot enabled and Windows installed as far as I know.
So what I did was in the Bios settings Boot/Secure Boot/Expert Key Management deleted all of the keys except the factory one (in my case the top one). Also with secure boot disabled.