OBS Studio Virtual Camera won't work

It turned out that disabling secure boot allowed modprobe to get the virtual camera to work. There may be another way to work this without disabling secure boot, but that worked for me. https://askubuntu.com/a/1198351/652 is the guide to disabling secure boot.

In my case (Ubuntu 21.04), this is related to the Secure Boot. Ange1ique's answer here worked for me. I will copy it to here, and add a clarification in case it helps others:

• uninstall v4l2loopback with: sudo apt-get remove --auto-remove v4l2loopback-dkms

• install v4l2loopback again with: sudo apt-get install v4l2loopback-dkms

• You will get a message about 'Configuring Secure Boot', which offers you the opportunity to create a key for this module. Read carefully and continue with tab(s) and an enter. Set the key/password and reboot.

• On rebooting enter the key/password in the Enroll MOK section, and continue the restart.

• enter this in the terminal: sudo modprobe v4l2loopback (don't know if this is necessary, but this time I didn't get an error)

• now install OBS or just run it if already installed.

I found a solution months ago on an OBS forum for the same problem which involved reinstalling OBS from ppa.

sudo apt update
flatpak remove com.obsproject.Studio
sudo add-apt-repository ppa:obsproject/obs-studio
sudo apt install obs-studio v4l-utils v4l2loopback-utils v4l2loopback-dkms

I also added some packages at the end to be sure no v4l2loopback package is left behind. In the case you don't have OBS installed with flatpak, just make sure these packages are installed and up to date:

sudo apt update
sudo apt install v4l-utils v4l2loopback-utils