On Fri, Jul 09, 2021 at 11:13:47PM +0200, Joerg Kampmann wrote: > Die folgenden Pakete haben unerfüllte Abhängigkeiten: > libavcodec-dev : Hängt ab von: libavcodec58 (= 10:4.1.6-dmo1+deb10u1) soll
There we have it. You have added a debian-multimedia (dmo) source intended to be used with Debian 10 (deb10). This is incompatible with Debian 9. You'll want to remove the inappropriate sources, as I said in my original reply. Then purge any and all packages that contain "deb10" in their version strings. That may not cure *everything* but it's a start.
