The Problem

So, this was my first time doing this. I prepared the bootable pendrive, followed the steps of installation and saw everything working fine using the preview feature, with the correct resolution: 1920x1080. The problem is: after i properly installed Ubuntu and rebooted my PC, the screen resolution dropped to 640x480 and the options to change that back are not available in the configs.

I’ve attempted finding a solution on my own, but everything I tried to do didn’t work and/or made things worse, to the point where it would not boot and I had to reinstall it. I decided, then, to look for help and ask a question here.

Thanks in advance!

More information

• Motherboard: Gigabyte Ga-78lmt-s2 Am3 Am3+ Fx 4100-Fx 8370e


• Graphic card: NVIDIA GeForce GTX 550 Ti

Running xrandr returns:

xrandr: Failed to get size of gamma for output default

Screen 0: minimum 640 x 480, current 640 x 480, maximum 640 x 480

default connected primary 640x480+0+0 0mm x 0mm

   640x480       73.00*

Running inxi -G returns:

Graphics: 

  Device-1: NVIDIA GF116 [Geforce GTX 550 Ti] driver: N/A

  Display: x11 server: X.Org 1.20.13 driver: fbdev,nouveau

  unloaded: modesetting,vesa resolution: 640x480~73Hz

  OpenGL: renderer: llvmpipe (LLVM 12.0.0 256 bits) v: 4.5 Mesa 21.0.3

Things i've tried

Solutions from https://snawarhussain.com/blog/ubuntu/linux/troubleshoot/ubuntu-20.04-resolution-stuck-at-1280-x-720/ alongside with Failed to get size of gamma for output default when trying to add new screen resolution.

xrandr: Failed to get size of gamma for output default still haunts.

• Edit_1:
  https://davidtsadler.com/posts/linux/2021-06-05/xrandr-failed-to-get-size-of-gamma-for-output-default/ also couldn't solve it for me. It does not seem to be what is causing my problem, since my GRUB_CMDLINE_LINUX_DEFAULT is already set to "quiet splash" from beggining.