Ok, that out of the way, I'll give you the same advice as I give everyone... wipe the USB stick and install Ventoy on it. It'll then have two partitions... one small partition with the Ventoy files, and one large blank partition.
Then download the Zorin OS .ISO file. Don't unpack it or uncompress it or mess with it in any way... just drop that .ISO file onto the large, blank partition. Name the .ISO file something intuitive (ZorinOS17.iso or somesuch).
While you're at it, download the Hiren's Boot CD Win10 PE .ISO and drop it on there, too (name it Win10PE.iso or somesuch)... just in case you need Windows (I use that to update the BIOS/UEFI and the trackpad firmware, since they're only provided in Windows-specific file formats).
Next time you boot, Ventoy will pick up that you've got bootable .ISO files available, and it'll pop up a menu allowing you to choose which .ISO file to boot.
I just keep that boot USB stick plugged into a USB hub, so I can easily boot the "LiveCD" version of Zorin OS to do full-disk backups. I've set up the Grub menu to include the Ventoy USB stick... it usually defaults to just booting Zorin OS from the hard drives after 10 seconds, but I can just change the menu selection to boot the USB stick.