Here's Debian's mirror btw, somewhat out of date and using the one-commit-per-upstream-release development model (in the upstream branch), so lacking a lot of history: https://salsa.debian.org/debian/youtube-dl
Youtube-dlc has merged a lot of youtube-dl's outstanding PRs, i remember -dlc being 350 commits/7 behind -dl some 2 or 3 days ago. So definitely base the fork off *-dlc
Here's Debian's mirror btw, somewhat out of date and using the one-commit-per-upstream-release development model (in the upstream branch), so lacking a lot of history: https://salsa.debian.org/debian/youtube-dl