I was on weekly 21.1.14 and after flashing 21.1.20 the Widevine on my device is now L3.
Edit:
Someone telled me on 21.1.20 thread about a re-upload of the rom zip with L1 libs.
Already downloaded it but Widevine still L3
MD5 is the same from the one I downloaded trough OTA.
Edit 2:
Yeah...