TeraByte Unlimited

I downloaded Mint Cinnamon 20.2 ISO
Used Rufus to make a GPT/UEFI UFD
Created a 20000 MB Linux partition using BIU
Booted the UFD in UEFI mode and installed to that partition as you did
On about the third screen, titled Multimedia Codecs, there is a greyed out "Configure Secure Boot" entry. I chose Continue.
Then chose Something Else
Ext 4 Journaling file system
tick in Format
/ mount point
EFI partition for Boot Loader
Needed to Reactivate BIU
The Boot File showed \EFI\ubuntu.005\shimx64.efi
Mint 20.2 booted

Do you have CSM disabled?

OK, so I loaded Mint Mate 20.2, shimx64 shows up, and I can boot to Mint. Perfect, in fact. I didn't even have to re-activate BootIt. Again, really appreciate your help Brian...you are a life saver.

My motherboard (ASROCK Z270 Extreme4) insists on having CSM enabled; it won't post if I disable CSM then goes into emergency mode and then posts back to setup screen in BIOS/UEFI, where I then have to change it back to CSM enabled.

I deleted the existing Mint partition and created a new partition to take it's place before I re-installed Mint Mate 20.2. The EFI partition still has the old boot file ubuntu001 that was established on partition that was deleted, and the new Mint partition is linked to ubuntu002. Not really critical, but how do I get rid of ubuntu001? I tried deleting it in BootIt but couldn't. If somehow I can, could I then re-name ubuntu002 to be ubuntu 001 and how would I do that without really screwing things up?

jaydub, while in BIU you could use TeraByte Explorer or Scripting to delete ubuntu.001

In Scripting....

RD \EFI\ubuntu.001 /s /y

If desired you could rename ubuntu.002 to ubuntu.001 with TeraByte Explorer or Scripting. Have a backup image of the ESP before starting this.