If Debian + Cinnamon fails, Debian + GNOME works, and Debian + GNOME + Cinnamon also works, then Cinnamon is not the cause per se.
After analyzing the differences between the packages in a Gnome + Cinnamon installation (functional) and those from Cinnamon alone (non-functional), the following two files were selected for installation : apt install bluetooth power-profiles-daemon After restarting and pairing, the audio connection via BT is stable and working !!! The two files are required to operate in either "hands-free" or "high fidelity" mode, as desired. If we remove one of the two modules, we’ll only be in hands-free mode... It seems that the maintainers of Linux Mint neglected this point, because this failure is also present in LMDE 7. Maybe Mint 22.x is also affected, I haven’t tested... I hope that this will be part of their procedures in the future. There is a sound quality issue with the audio codec in SBC-XQ, we hear crackles, it looks like there are micro cuts. SBC work fine. I was able to activate LDAC, everything works :)
