Those with excellent memories may remember Gabe Newell alluding to three Valve VR games back in 2017. That was long before Half-Life: Alyx was announced, and a lot can change in three years. As of now—and immediately following the release of Half-Life: Alyx—the company doesn't have two other VR games in active development.
Speaking to Upload VR, Valve designer Greg Coomer said that most of Valve's VR development resources moved to Half-Life: Alyx late in its development cycle. "So at the moment, no, there aren’t three other titles in development," he said. "But, as for what’s coming, we don’t really have something new or newsworthy for you to say: ‘Once Alyx is out the door here's what you should expect to have happen.'" (Meaning we shouldn't have any specific expectations right now.)
In 2017, Newell stopped short of saying any of these three games were in active development. "We think we can make three big [virtual reality] games,” he said back then, so there's every chance the other two were left on the cutting room floor. That said, Upload VR reports that another Valve developer, Jason Mitchell, said he'd worked on a Valve VR project that wasn't The Lab or Half-Life: Alyx.
Overall, Valve is keeping typically vague on its VR future: whether future Half-Life games will dip back into VR will depend on how Alyx is received. If critical reception is any indication, it's being received well: In his review, Chris wrote that "revisiting City 17 in VR is a thrill in Half-Life: Alyx".