Yes, synching channels does not appear to work. The communities/channels are not updated, but the posts basically work if you or somebody else on your platform enter the URL of a video into the search.

Even if it would work, it probably would not update since nobody on your instance subscribed and I don’t think Lemmy federates posts of communities that aren’t subscribed. But I’m not sure how it is now.

That the comments don’t seem to work is odd indeed.

You can interact with any video and comment.

I just threw the link of the newest video into the search of my instance: https://discuss.tchncs.de/c/spacequesthistorian@spectra.video

It has one comment because I actively put https://spectra.video/w/aTouTCEzdPEdWuwsYU8LQZ;threadId=59658 into the search

Edit: I opened an issue for starting commenting from PeerTube, since that seems to be broken

I can't show you directly, as fedia.io requires login to access the platform (scraper protection), but I was able to open the channel by searching for their handle, the page showed up videos (also recent ones) and the video-posts had comments. The page show the channel-logo and every post had the thumbnail of the video.
One click on the title when you have to post open, and it will open the original page in a new tab, which then can play the video. Even better: Mbin automatically inserts the embedded viewer for the posted video, so you don't even have to leave fedia.

So please don't draw conclusions from Lemmy to all fedi projects.