This was somehow working yesterday, but as of today, if my son logs into the Launcher with his Microsoft family account (the primary has PC Game Pass), Java Edition only shows "Play Demo" where as Bedrock and Dungeons recognize the game pass.

If I switch account to the primary Microsoft account, then all 3 (Java, Bedrock and Dungeons) recognize the game pass.

Seems there are multiple reports of Java + Game Pass showing Play Demo only, but the tickets keep getting merged to one from November.  This worked fine yesterday, so something seems to have changed.