Install mono using the below:

sudo apt install ca-certificates gnupg
sudo gpg --homedir /tmp --no-default-keyring --keyring /usr/share/keyrings/mono-official-archive-keyring.gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb [signed-by=/usr/share/keyrings/mono-official-archive-keyring.gpg] https://download.mono-project.com/repo/ubuntu stable-focal main" | sudo tee /etc/apt/sources.list.d/mono-official-stable.list
sudo apt update
sudo apt install mono-devel

then run with:
sudo mono LightgunMono.exe

You can edit settings in LightgunMono.exe.config but the default should work well.

If both lightguns don't work together, try another USB port, ideally on a different usb controller, so either further away or one that is black and one that is blue.


