To anyone this may help, removing hc4 related packages and replacing them with c4 packages did the job.
Only to discover that, for whatever reason, I actually had an HC4 board and convince myself that it was a C4 ...
Anyway, the reverse process also worked as expected and my board is now running 25.051.1 happily, except for the samsung SSD not recognized at boot, and requires to be hot plugged just after the linux kernel starts in order to be seen by the system, as it is described in other threads.
