I can explain.
This is actually my bug report: 1902269
I’ve been asked in this discussion to file it and here it looked like it could be related to the topic.
I didn’t post that link because the bug is marked as duplicated of this other 1901137… “grub-install fails due to no space left on ESP”.
But ‘no space left on ESP’ is not the problem I’m talking about. What I’m talking about is that there should NOT be any ESP at all on a old bios system.
If there is an ESP partition, then you make Ubuntu incompatible in many use cases with non-uefi systems.
That’s why I have posted that link to a still open bug, which basically describes the same thing that I and other users have experienced.
(I haven’t see anyone having no problems in those use cases).
Is that off topic? Maybe.
I’m sorry and apologize for that.
I didn’t want to post here. I tried to find a way to rise the problem so that some of the staff could at least mention this (big) problem on the 21.04 release notes.
If there had been a way to do it directly I would have done it, giving all the possible information. I’ve spent hours and hours testing all the use cases and writing down a wiki page (on ubuntu-it wiki) with every combination to make life easier especially to newcomers. So they can easily see if their case is one of the possible case that leads to an unbootable computer.
And thanks godness this is not happened with an LTS version. It could have been a carnage…