You mean you want to mirror your YouTube comments and let people comment on the mirror site? Or do just mean self-host downloadable videos. The latter is easier.

Peertube with a default upload quota of 1kb for new users?

I think Peertube would be overkill for a single channel, but it's the closest to YouTube in terms of features (multiple formats/transcoding, comments, etc). Otherwise I would just rip the channel with yt-dlp and setup a "mirror" on something simple like a static site or blog. Find something that works, then automate (a simple shell script + cron job would do the trick).

https://github.com/tubearchivist/tubearchivist, maybe?