I can bring up the grub menu on startup. The problem is that I only see kernel 6.5 in the advanced options. The kernel 6.6 installed next to it is not even displayed for me to select!
This is probably because I still had an outdated Live USB stick from which I just reinstalled Manjaro on my notebook.
I can’t activate kernel 6.6 to start Manjaro! Can you help me, what is to do?
When you reinstalled last time, you corrupted your system somehow.
(Only you know what you did then)
So now your grub is disconnected with its actual configfile (grub.cfg).
There is one place where your system installs the kernels. And then grub creates a new configfile including these kernels.
But the booting grub does look into an “very old” configfile somewhere, where it has been left after your last install.
At least you will need to reinstall grub, so it is again connected to the actual configfile.