He said that there is maybe a bug in Ubuntu because the previous firmware I used from John Lewis doesn't re-run the video BIOS when switching to SeaBIOS. He'd guess it has to do with the way JL's SeaBIOS reuses the existing framebuffer vs re-initializing using the VGA BIOS.
Thanks to MattDevo I managed to fix the problem by installing his legacy firmware :
https:/ /github. com/MattDevo/ scripts
He said that there is maybe a bug in Ubuntu because the previous firmware I used from John Lewis doesn't re-run the video BIOS when switching to SeaBIOS. He'd guess it has to do with the way JL's SeaBIOS reuses the existing framebuffer vs re-initializing using the VGA BIOS.