I wish v4l2loopback was included in the kernel. I've wasted far too much time messing about with DKMS in the past that I now avoid any out-of-tree modules if I can avoid it. And with Secure Boot they become untenable.

To be fair there is an issue tracking progress - https://github.com/umlaeute/v4l2loopback/issues/268 - but it's had no updates in 18 months.