Need help on deploying bullseye

Hi,
I have herited of an already FAI setup that deploy debian buster using pxe
and it works great!
Now, I try to use it to deploy bullseye but even if I have ready the
documentation I am still not sure how to proceed with the correct steps...
Should I modify the existing config or create a new one dedicated to
bullseye and point my server pxe boot to this one?
Even if I set /srv/fai/config/class/DEBIAN.var with release=bullseye it's
not working..
Let me know if you want me to share some config files.

Any help will be greatly appreciated :)
Thanks!