Did a search for ubuntu "integrity: problem loading x.509 certificate" and the first result indicates out of date bios certificates needed for secure boot on older laptops. Disabling secure boot seems to be the suggested fix.
darcmage
joined 1 year ago
I tried downloading from the link provided and it started downloading the file for me.
Wouldn't getting something like a Kobo and syncing with Calibre be a much easier/cheaper option?