Xubuntu installation: “ERROR atombios stuck in loop for more than 5secs”

I am trying to install Xubuntu 20.04 from a Live USB prepared with the Startup Disk utility. When I boot from it, the Xubuntu logo appears and the USB check is performed.

Once the check says OK, the screen stays the same for about a minute and then suddendly the logs appear with an error:

...
[ 190.290327] kernel: [drm:atom_op_jump [radeon]] ERROR atombios stuck in loop for more than 5secs aborting
[ 190.290351] kernel: [drm:atom_execute_table_locked [radeon]] ERROR atombios stuck executing D1F6 (len 62, WS 0, PS 0) @ 0xD212
...

At this point, the boot does not advance and continues to print the same error again and again.

I read a post with a similar issue. It suggested to add a GRUB option:

amdgpu.dc=0

However, I am a complete newbie on this kind of things. Where should I add that line? Is it the right thing to do? Consider that I am still trying to boot from the USB for installing the OS.

My computer is a HP Envy 17 Notebook PC bought in 2010. I already have Ubuntu 18.04 installed.

Thank you very much for your help.