This bug seemed similar to: shim-signed 15.4 does not boot on EFI 1.10 systems: 1925010
The above bug was fixed with a change to package shim-signed.
The version of shim-signed for Ubuntu 20.04 was last changed in August 2020. This is three months before the problem showed up. So, unless the change was stuck in a three month long queue before being sent out, it is not likely the same problem.
This bug seemed similar to: shim-signed 15.4 does not boot on EFI 1.10 systems: 1925010
The above bug was fixed with a change to package shim-signed.
The version of shim-signed for Ubuntu 20.04 was last changed in August 2020. This is three months before the problem showed up. So, unless the change was stuck in a three month long queue before being sent out, it is not likely the same problem.