Just to remind you of my earlier post.
I installed an fresh Linux Mint 20.1 and had no difficulty getting everything needed. The version libc6 is 2.31-0ubuntu9.2. Thats the same version in U20.04 which, as we know, Mint is based on. Your install wanted ~0ubuntu9.3.That means, to me, very few possible explanations -
1. 'Someone' repackaged it, realised their mistake and reverted it. The number change, 2->3 is a packaging revision. Ubuntu would not, at the point of a gun, do something like that to their flagship LTS version.
2. Alternatively, your local system was, at some stage, 'forced' to update libc6 to a later version than it should be using (although again, only a packaging revision ??)
Both seem quite unlikely. Frankly, I suggest we regard the problem solved and keep our own council.
Mind you, specifying packaging versions in a dependencies list certainly contributed to this problem. But as libc is critical to the entire OS, I sort of understand Ubuntu's obsession.
Davo