How to format a USB drive and increase its available size?

I don’t know a good way to test disks for sizing without a third party program or command line tools.

The former, I use SD Clone: https://twocanoes.com/knowledge-base/sd-clone-3-getting-started/

The latter - try these commands once you get the unix disk number from Disk Utility or another means - be 100% sure you have a backup of every single drive connected. If you get the drive number wrong (in the linked question the USB drive to be erased is disk3 and those numbers can change each time you eject and mount a drive), you will erase without a chance of recovery whichever drive you perform this on:

diskutil list diskX
diskutil eraseDisk JHFS+ TestDisk disk3
diskutil list diskX

When I say “be sure of your backup”, that you have set aside the time and steps needed to restore that backup - not just “maybe it’s current and I haven’t checked it for a while” type backup. Hopefully it’s a quick erase and not that the disk itself is broken or mislabeled.

If you can you might trying erasing the disk and then reformat it. You will, of course, lose everything written to disk. If you want to keep what's on the disk you could copy it you main drive. Disk utility allows you to erase the disk and then reformat it.

After opening Disk Utility go to the Edit menu and at the top of the panal you'll see option to erase, partition, and other commands.