Because I had some problems with recent hw, drivers, I decided to see if it improves with the latest kernel.
As this does not solve the problem either, I uninstalled the kernel again using kde system settings - kernel.
The kernel is uninstalled, but grub still lists it and it also takes this uninstalled kernel as the default startup option (also after a manual grub update).
Afterwards I also followed these instructions, https://wiki.manjaro.org/index.php/Manjaro_Kernels#Removing_Kernels
All commands indicate that the kernel is no longer installed, but still it is listed in the grub boot menu.
So apparently the uninstall instructions and the system settings uninstall script is not complete, as they don’t take care of the grub menu.
How can I remove these lines in the grub menu from the uninstalled kernel, in a way that the command sudo update-grub creates the grub menu correctly, without the uninstalled kernel lines, and without making the uninstalled kernel the default boot option ?