Find the line beginning
GRUB_CMDLINE_LINUX_DEFAULT and add the text
amdgpu.dc=0 between the double quotes (
""). Leave any other parameters as they are. For example, you may end up with a line like this:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash amdgpu.dc=0"
Save the file and exit, and then run
to write the configuration, and reboot.