This is the introduction.
Which, on a modern hybrid system, will get you to PRIME.
Which by default is iGPU, but dGPU when you use prime-run.
From there you can opt to further modify things, such as by steps like found
Though I cant attest to the actual quality of that guide.
It woud appear to be for xorg only, at least as written, so thats a factor.
They are entirely different, though you could see the archwiki as a possible ‘expansion’ of the manjaro guide.
Depends on your system. Like which display manager.
But if you just want something easy then you can use envycontrol.
It is a switcher utility allowing you to reboot into iGPU-only, dGPU-only, or hybrid (how prime already is without a switcher tool). There are also complimentary GUI apps and widgets for it so you can do that select-reboot right from a panel menu item.