Done!
Thank you @Mirdarthos
I installed the latest LTS Kernel, took the risk and played with Grub (I have a grub menu now).
I also searched the forum and doublechecked How to make a Kernel default? - #3 by linux-aarhus
Now:
uname -a ✔
Linux manjaro 6.6.46-1-MANJARO #1 SMP PREEMPT_DYNAMIC Wed Aug 14 17:17:23 UTC 2024 x86_64 GNU/Linux
~ mhwd-kernel -li ✔
Currently running: 6.6.46-1-MANJARO (linux66)
The following kernels are installed in your system:
* linux66
* linux69
~ pacman-mirrors --get-branch ✔
stable
~
I think it is OK now I am on the latest LTS kernel, on stable repos.
I double checke as well that AUR is disabled!
So my system is the most possible stable system.
Thank you all for your support and for Manjaro!