This December update was quite significant, as I know a few peoples sites tanked as well, so you're not alone.
I still think the main problem for you is thin content. Google doesn't seem to be as strict as they are about duplicate content. But if you're taking the movie/episode description from TMDb, there are most likely thousands of other sites doing it too.
Google could have put you in a category of thin content [1], you may have got a notification in Search Console (but unlikely, I'm not a fan of the new Search Console since literally all the data in there is so vague which makes it not very helpful).
Another thing is that when I look in Ahrefs for pages with the most links [2], they are forum profiles that have been hit with spammy Xrumer/GSA link. They're referred to as profile links. They are pretty useless, but people still build them as there is literally $0 cost to do so.
If I were to offer my advice, my first step would be to build some content. First, add some content on the homepage (if you get SurferSEO it will tell how many words to write based on your competition) and then if you're willing to build a blog in (you seem to be a developer). You could write some roundup articles that are SEO focused and then link to the relevant Show/Movie, which would also help your internal linking.
If you wanted to explore building backlinks (depending on if you want to go on a whitehat or greyhat road) - you can look into paid guest posts or niche edits.
[1] https://www.vertical-leap.uk/blog/what-is-thin-content-why-d...
[2] https://i.imgur.com/xZ8VEJQ.png