sudo apt update
Fehl:1 http://ftp.de..debian.org/debian buster InRelease
  »ftp.de..debian.org« konnte nicht aufgelöst werden.
Holen:2 http://security.debian.org/debian-security buster/updates InRelease [65,4 kB]
Holen:3 http://deb.debian.org/debian buster-backports InRelease [46,7 kB]                                              
OK:4 http://repo.steampowered.com/steam precise InRelease                                                                              
Holen:5 http://security.debian.org/debian-security buster/updates/main Sources [101 kB]                      
Holen:6 http://ftp.de.debian.org/debian buster InRelease [122 kB]                   
Holen:7 http://security.debian.org/debian-security buster/updates/non-free Sources [692 B]                  
Holen:8 http://deb.debian.org/debian buster-backports/main amd64 Packages [128 kB]
Holen:9 http://security.debian.org/debian-security buster/updates/main i386 Packages [146 kB]
Holen:10 http://security.debian.org/debian-security buster/updates/main amd64 Packages [147 kB]                    
Holen:11 http://security.debian.org/debian-security buster/updates/main Translation-en [74,2 kB]                           
Holen:12 http://security.debian.org/debian-security buster/updates/non-free i386 Packages [552 B]                         
Holen:13 http://security.debian.org/debian-security buster/updates/non-free amd64 Packages [552 B]        
Holen:14 http://security.debian.org/debian-security buster/updates/non-free Translation-en [344 B]        
Holen:15 http://deb.debian.org/debian buster-backports/main i386 Packages [127 kB]                        
Holen:16 http://deb.debian.org/debian buster-backports/main Translation-en [105 kB]
Holen:17 http://ftp.de.debian.org/debian buster-updates InRelease [49,3 kB]                                        
Holen:18 http://ftp.de.debian.org/debian buster/main i386 Packages [7.864 kB]
Holen:19 http://ftp.de.debian.org/debian buster/main amd64 Packages [7.908 kB]
Holen:20 http://ftp.de.debian.org/debian buster/main Translation-en [5.969 kB]
Holen:21 http://ftp.de.debian.org/debian buster/main Translation-de [1.654 kB]
Holen:22 http://ftp.de.debian.org/debian buster/main Translation-de_DE [830 B]
Holen:23 http://ftp.de.debian.org/debian buster/main amd64 DEP-11 Metadata [3.807 kB]
Holen:24 http://ftp.de.debian.org/debian buster/main DEP-11 64x64 Icons [7.596 kB]
Holen:25 http://ftp.de.debian.org/debian buster/main DEP-11 128x128 Icons [12,8 MB]
Holen:26 http://ftp.de.debian.org/debian buster/non-free i386 Packages [76,2 kB]
Holen:27 http://ftp.de.debian.org/debian buster/non-free amd64 Packages [88,0 kB]
Holen:28 http://ftp.de.debian.org/debian buster/non-free Translation-en [88,7 kB]
Holen:29 http://ftp.de.debian.org/debian buster/non-free amd64 DEP-11 Metadata [9.096 B]
Holen:30 http://ftp.de.debian.org/debian buster/non-free DEP-11 64x64 Icons [38,3 kB]
Holen:31 http://ftp.de.debian.org/debian buster/non-free DEP-11 128x128 Icons [6.725 B]
Holen:32 http://ftp.de.debian.org/debian buster/contrib amd64 Packages [51,0 kB]
Holen:33 http://ftp.de.debian.org/debian buster/contrib i386 Packages [46,9 kB]
Holen:34 http://ftp.de.debian.org/debian buster/contrib Translation-en [44,7 kB]
Holen:35 http://ftp.de.debian.org/debian buster/contrib amd64 DEP-11 Metadata [11,5 kB]
Holen:36 http://ftp.de.debian.org/debian buster/contrib DEP-11 64x64 Icons [110 kB]
Holen:37 http://ftp.de.debian.org/debian buster/contrib DEP-11 128x128 Icons [226 kB]
Holen:38 http://ftp.de.debian.org/debian buster-updates/main Sources [2.544 B]
Holen:39 http://ftp.de.debian.org/debian buster-updates/main amd64 Packages [5.792 B]
Holen:40 http://ftp.de.debian.org/debian buster-updates/main i386 Packages [5.788 B]
Holen:41 http://ftp.de.debian.org/debian buster-updates/main Translation-en [3.655 B]
Es wurden 49,5 MB in 6 s geholt (7.608 kB/s).                                                                                                                                          
The AppStream system cache was updated, but some errors were detected, which might lead to missing metadata. Refer to the verbose log for more information.
Paketlisten werden gelesen... Fertig
W: Fehlschlag beim Holen von http://ftp.de..debian.org/debian/dists/buster/InRelease  »ftp.de..debian.org« konnte nicht aufgelöst werden.
W: Einige Indexdateien konnten nicht heruntergeladen werden. Sie wurden ignoriert oder alte an ihrer Stelle benutzt.
E: Problem executing scripts APT::Update::Post-Invoke-Success 'if /usr/bin/test -w /var/cache/app-info -a -e /usr/bin/appstreamcli; then appstreamcli refresh-cache > /dev/null; fi'
E: Sub-process returned an error code

user@debianPC:~$ sudo apt update
OK:1 http://deb.debian.org/debian buster-backports InRelease
OK:2 http://ftp.de.debian.org/debian buster InRelease                     
OK:3 http://security.debian.org/debian-security buster/updates InRelease  
OK:4 http://ftp.de.debian.org/debian buster-updates InRelease                
Holen:5 http://ftp.de.debian.org/debian buster/contrib Sources [43,1 kB]     
OK:6 http://repo.steampowered.com/steam precise InRelease                                          
Holen:7 http://ftp.de.debian.org/debian buster/main Sources [7.832 kB]       
Holen:8 http://ftp.de.debian.org/debian buster/non-free Sources [86,3 kB]
Es wurden 7.962 kB in 1 s geholt (5.211 kB/s).           
The AppStream system cache was updated, but some errors were detected, which might lead to missing metadata. Refer to the verbose log for more information.
Paketlisten werden gelesen... Fertig
E: Problem executing scripts APT::Update::Post-Invoke-Success 'if /usr/bin/test -w /var/cache/app-info -a -e /usr/bin/appstreamcli; then appstreamcli refresh-cache > /dev/null; fi'
E: Sub-process returned an error code