I downloaded YUMI UEFI and put Linux Mint on the flash drive. During the process I wiped the drive and formatted FAT32A. I made the flash drive first in my Boot Order. It won't boot.

I like YUMI, but I recommend Ventoy or E2B (Easy2Boot) as better options. Warning: the E2B site is add heavy, so you want an add blocker in place.

With Ventoy you use the Ventoy software prep script to prep a USB thumb drive. You can select if you want EFI support on the thumb drive, and I do recommend that. Then just copy the ISO file(s) onto that thumb drive. (You can add as many ISO files as you have room for, but I recommend not filling it all the way.) When you boot from that device you get a menu of the available distributions (ISO files) to load.

I normally carry one such thumb drive in my keychain and have two others I load and carry in pocket if I need to do installation, troubleshooting, or network analysis work.

I've not used the software mentioned above but see the Mint site recommends Etcher. Maybe more information on what happens would help someone to help you as 'it won't boot' is very vague. Do you see any messages on screen when you try to boot? Do you have another computer you can use to test to see if the usb boots to eliminate that as a problem.

Ventoy worked for me after I disabled Secure Boot.

If doing this on a windows system lots of options, besides what is already mentioned there is also rufus https://rufus.ie