how to install gcc-6 in debian bullseye

Can anyone kindly instruct me how to install gcc-6 in Debian 11? I need compile a software and was hinted gcc version (10) is too high. I have old machine with gcc 6 and was able to compile it there. Thank you very much. Michael

plugged and unplugged monitor

I have a linux machine for scientific calculations with GPU installed. It also installed GUI but normally the default start mode is just terminal (multi-user.target). If I start up the machine with a monitor plugged into the GPU (HDMI or Displayport), the monitor works well (showing the