Looks like Stadia is upping the count on Stadia Pro games again - with five initial games announced for December. Not that these announcements are ever comprehensive; Stadia is known for surprising Pro members with sneak drops almost every month. For example, Wavetale got added to Stadia Pro in November with zero warning that it was coming.
So, while we suspect there will eventually be more, for now the announced Stadia Pro games are as follows:
Destroy All Humans
Falconeer Warrior Edition
As a reminder, Stadia Pro games are available to all Pro members so long as their membership is current. If you leave and come back, your Pro games will be waiting there for you, much like the way that PlayStation handles Plus games.