There are quite a few other forum threads that explain that Canonical is messing with things due to the priority on their Ubuntu ESM repository and that you need to further mess with priorities to get Incus to correctly install from an external repository on such systems.
Another nice way on creating a live boot OS is using GRML. It is based on Debian Trixie on default and has an option to add ZFS into the CD or USB build. You might properly be able to add Incus to it with a custom module, should try this the next time I build one
Can provide some more details if there is interest.