I have a similar problem like "solus-enroll not recognized as valid certificate"
On my laptop (Lenovo) I don't have the MOK blue screen but I can manage secureboot keys in UEFI Bios.
I can add :
- Platform Key (PK)
- Key Exchange Key (KEK)
- Authorized Signature Database (DB)
All accept to load the solus-enroll-me.cer
but the Key manager asks me to enter a "SignatureOwner GUID" see picture.

I don't know what to do with that...
When I let GUID to 0, it appears to successfully enroll the cert. But when I restart it say "invalid signature"
Thanks for help
Regards,