I'm hoping part of Barr's leaving wasn't related to something like "I can't have anything to do with this list of pardons this jackass wants to run out there."
Probably I don't want to see a list of those proposed pardons, and I don't know what to think about advice Trump will get on them from DOJ's Office of Legal Counsel under Rosen as AG now.
People are talking about Barr having been canned and so forth, and Trump writing that lackey-style resignation letter for him to sign. But Barr was likely getting exasperated by what all Trump was wanting to do lately, a lot of it just wanting to burn the house down in his rage over losing re-election. We probably don't know the half of it.
Also Barr still probably had a few more things he wanted to do to re-org the DoJ to make it less independent and more under control of a strong executive branch... having to spend time babysitting Trump's doubtless illegal brainfarts about "oh i know what i could do next to fix Biden's wagon, I could yada yada..," was probably maddening.