So this has been something Ive been trying to get working right for days, i tried to get early KMS and any other possible ways of getting high resolution console at boot time with an Nvidia GPU, specifically a 1080ti. Finally i have managed to do it though and ill share how as its really simple if youre willing to use UEFI over Legacy mode. I was in legacy mode so had to switch my system to GPT/EFI which is a fairly simply but time consuming process.
The problem ends up being having CSM support enabled to allow legacy operation. When you have CSM enabled the Nvidia GPU will default to legacy mode and limit you to a max of 1280x1024 resolution. This is due to Nvidia not providing fbdev so you are limited to VGA resolutions and Nvidia will mostly likely never touch this so you NEED to use UEFI to get HighRes.
If you install your Manjaro/Linux system in UEFI mode, disable CSM and make sure youre in a pure UEFI only mode, your Nvidia GOP driver will work in efifb mode which will allow you to have native grub/terminal resolutions which you can set the usual way in /etc/default/grub, i.e GRUB_GFXMODE=2560x1440x32 GRUB_GFXPAYLOAD_LINUX=keep
This wasnt easy for me to find or figure out as i couldnt really find much searching so i started experimenting and looking into efifb and how to get it working. Hope this helps someone get it working also and any questions id be happy to answer.