It looks like the latest release (https://github.com/obsproject/obs-studio/releases/tag/26.1.0) has this included.
- Bug#960342: obs-plugins: Please include v4lsink... Michael Gebetsroither
- Processed: Re: Bug#960342: obs-plugins: Pl... Debian Bug Tracking System
- Bug#960342: obs-plugins: Please include v4... gregor herrmann
- Bug#960342: Bug#975282: RFP: obs-v4l2sink ... Martin
- Bug#960342: Bug#975282: RFP: obs-v4l2sink ... gregor herrmann
- Bug#960342: Bug#975282: RFP: obs-v4l2sink ... James Tocknell
- Bug#960342: marked as done (obs-plugins: P... Debian Bug Tracking System
