Just to confirm, when you say it doesn't boot after the patch yesterday: this means you had 21.04 installed, and the system did boot with 15.4-0ubuntu1, but now does not boot with 15.4-0ubuntu2?
Just to confirm, when you say it doesn't boot after the patch yesterday: this means you had 21.04 installed, and the system did boot with 15.4-0ubuntu1, but now does not boot with 15.4-0ubuntu2?