Hello @Haris Papageorge ,
Microsoft is switching over to the 'DigiCert Global G2 root' certificate for TLS traffic.
This means that your IoT devices must include 'the DigiCert Global G2 root cert by February 15, 2023'.
It seems you use x509 self-signed certificates to identify your devices. Your self-signed certificate is just an Identity, it is not used for encrypting the TLS traffic towards IoT Hub and/or DPS.
It's all about testing the TLS connection using that root certificate. That is why the symmetric key (SharedAccessKey) test is offered.
See also the comments below the announcement text.