Thank you for releasing Kavita and Komga! To add the right metadata to e.g. mangas there is a wonderful tool called „komf“, which also has a docker compose file. (the data is written as comicinfo.xml into the cbz files)
URL: GitHub - Snd-R/komf: Komga and Kavita metadata fetcher
When the container is running, there can also be a userscript added to trigger komf - otherwise afaik a cronjob or similar is needed.