[Solved] rpi 4 does not use full 4k screen resolution

[freeTheHeel]

I ran into issues when trying to use my rpi4 with a 4k display resulted in a lower 1080 screen resolution and large black bars on the side of the screen. I tried a lot of mucking around in config.txt trying to adjust the various overscan options and other false leads with xrandr but none of these seemed to fix the issue.

In the end I pulled the following out of the default config.txt for the raspian and they seemed to fix the problem for me:

$this->bbcode_second_pass_code('', '
disable_overscan=1

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
dtoverlay=vc4-fkms-v3d
max_framebuffers=2
')

I hadn't seen any other posts in my searches to find a solution to this so figured I would post here in case it helps someone else out in the future.