I'll provide some detail from my last comment

With regards the ESP (EFI system partition) flag not being set, I'll provide a link to an answer which shows what I do - https://askubuntu.com/questions/1273...276789#1276789

Note: some boxes require that to be done, others do not (thus the may fail to start warning)

Yeah the ESP (EFI system partition) message isn't helpful for end-users given no check box is present to select that (correct names are used which results in a mis-match between what is called ESP in one later standard; but as the concept of ESP didn't exist when the prior standard was written it's called something different by that standard being flag names on partition table dialog). I'm hoping my askubu link will suffice.

Hopefully you got it sorted by the help others provided...

FYI: if you follow the manual link (on askubu page); stable refers to the latest release which currently is groovy or 20.10, so replace the "stable" in the URL to say "lts" and you'll get the manual page for focal or 20.04 LTS