You have a couple of options
- Manual install to USB [root tip] Do a manual Manjaro installation
- Manual install using LUKS [root tip] Manjaro-To-Go LXDE with persistance
- Use
ventoy(available in repo) use the data partition option - https://ventoy.net - Use the mbusb script - https://mbusb.aguslr.com/
- [root tip] Multi ISO USB with storage partition