CleUSB -
EFI -
ISO -
Linux -
Ventoy -
Ventoy is an open source tool which creates a special USB stick.
That stick contains an exFAT partition in which you can copy multiple ISO files and an EFI partition where Ventoy puts its bootable menu.
When you boot on the Ventoy USB stick, the menu lists all the ISOs you placed in the exFat partition and you can boot any of them.