The system I have run my test conversion on was not easy.
Because Manjaro has many different kernels the nvidia drivers are closely connected to the kernel.
The process included reverting to the nouveau driver - rebooting - replacing the kernel with Arch stock kernel - rebooting - and ensuring your system is running using the free driver.
When you have the free driver running - you can install the nvidia driver - reboot - run nvidia-xconfig as root which will create a default config in X11 named xorg.conf.
Then copy that config to /etc/X11/xorg.conf.d as 20-nvidia.conf - and reboot (recommended on arch wiki).
The run nvidia-settings to create a more customized version (if you run as root you can replace the 20-nvidia.conf with the new file you are createing).
Also to note, as the Nvidia guide link above suggests, if you want to use a kernel that is not standard, such as the ‘zen’ kernels, you need to install ‘nvidia-installer-dkms.’