Install ventoy and do the option to preserve data at the end of the usb stick.I did that with Kali on my USB stick to have a system with persistence:
Workaround: Installation of Kali next to ventoy partitions Perhaps it is possible to install another multi-boot system on that partation, but I don't know if it works. With ventoy application you could preserve space on your USB stick and install a linux system on that partition next to ventoy. It will not work as long as does not fix it.
