Can I introduce you to a so called Eierschalensollbruchstellenverursacher?

No, we only use Jellyfin via browser. Unfortunately even with imported Client Cert, Android apps won’t work.

Edit: Client Certs need to be implemented per App. There is a feature request from 2022 https://features.jellyfin.org/posts/1461/capability-to-specify-client-certificate-for-android-client

There is a good reason I only have Jellyfin and other services accessible via valid Client Certificate.