https://cdimage.debian.org/debian-cd/current/amd64/iso-cd/debian-12.5.0-amd64-netinst.iso

I was booting in expert mode and expecting between the mirror select
and the installing of the base system there to be an option to select
which release to install (oldstable, stable, testing, unstable), as
I have been using occasionally for years.

This menu did not show up.