Hello
I have a question Is it possible to manually install the latest kernel? So without da GUI Since I like to use the kernel 5.15.8 and this is yes unfortunately not yet in the GUI to find. I am still new to Manjaro please do not be too hard haha
5.15.8-1 was just built and will be available in the unstable branch soon.
As far as I know if you install the latest kernel and reboot, Manjaro will automatically use it.
https://wiki.manjaro.org/index.php/Manjaro_Kernels#Terminal_Commands
If you mean latest-latest kernel - as in latest stable/mainline/longterm on kernel.org - you have to switch your branch to unstable.
sudo pacman-mirrors -aS unstable
Then run a sync-database-system and your installed kernel is synced to the latest available for a Manjaro system.
sudo pacman -Syyu