Well I saw this coming a mile away when Scale became a thing:

https://pcper.com/2024/03/truenas-core-bids-g … bye-to-freebsd/

TRUENAS CORE JOINS SCALE IN USING DEBIAN The current TrueNAS CORE 13 will be the last FreeBSD-based NAS from iXsystems. From no […]
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TRUENAS CORE JOINS SCALE IN USING DEBIAN
The current TrueNAS CORE 13 will be the last FreeBSD-based NAS from iXsystems. From now you will see the OS of the popular NAS software switch to Debian, but it’s necessarily bad news unless you are a FreeBSD lover. The use of the OpenZFS file system means you can do an in place migration to the new OS, though it is a one way transition. There is one small hiccup though, VM appliances will not be able to migrate along with your data.

TrueNAS CORE plugins run in FreeBSD jails, the new version will use the built in Linux kernel’s KVM and unfortunately there is no way to move your VMs from one to the other. There will be one final TrueNAS CORE 13.3 update with fixes for ZFS and Samba to match TrueNAS SCALE so you have a bit of time before you have to think about migration.

The Register has a list of some other hoped for features in TrueNAS CORE 13.3 as well as some details on the timelines you should be aware of.