No download because of missing key?

Hello and kind regards again.

Im am running my Plex Media Server on a 16 GB Raspberry Pi 5, Raspbian Trixie. Since one or two days every update process invoked by using

sudo apt update && sudo apt dist-upgrade -y

throws ma an error message of this style (sorry, some parts in german);

OK:5 https://downloads.plex.tv/repo/deb public InRelease
Fehl:5 https://downloads.plex.tv/repo/deb public InRelease
Sub-process /usr/bin/sqv returned an error code (1), error message is: Missing key 97203C7B3ADCA79D, which is needed to verify signature.
OK:6 Index of /debian trixie InRelease
Paketlisten werden gelesen… Fertig
W: Whrend der berprfung der Signatur trat ein Fehler auf. Das Depot wurde nicht aktualisiert und die vorherigen Indexdateien werden verwendet. OpenPGP-Signaturberprfung fehlgeschlagen: https://downloads.plex.tv/repo/deb public InRelease: Sub-process /usr/bin/sqv returned an error code (1), error message is: Missing key 97203C7B3ADCA79D, which is needed to verify signature.
W: Fehlschlag beim Holen von https://downloads.plex.tv/repo/deb/dists/public/InRelease Sub-process /usr/bin/sqv returned an error code (1), error message is: Missing key 97203C7B3ADCA79D, which is needed to verify signature.
W: Einige Indexdateien konnten nicht heruntergeladen werden. Sie wurden ignoriert oder alte an ihrer Stelle benutzt.

Looks like the gpg signature of Plex can not verified because of a missing key. The result of that: i can not reach the Web player in my local network anymore although the Raspberry Pi itself runs fine. The odd thing: I still can use the Plex Amp app on my mobile devices.

Does anybody know what to do about this missing key?

Thanks in advance for any possible reply!

Jens