Sorry, my last message was indeed ambiguous. The list showed the non-free packages on my PC *before* I removed them all. In fact, I even added #non-free-firmware as a comment in /etc/apt/sources.list and performed an update, etc., in order to have a completely free system.
And with the 6.12.48+deb13-amd64 kernel reinstalled, my system is rock solid again (no crashes or problems in a week of use).
So, in reality, the problem comes from amd64-microcode, what else? If case you want to reassign this bug. For my part, I will no longer use non-free packages.