It's Lean D for now but I wouldn't put it entirely past the GOP to pull another hat trick.
This race is the safest Governor's race in the country for the Democratic Party. No realistic combination of candidates could result in the Republican candidate being competitive. Maryland was already one of the bluest state's in the country, but then stampeded further Left partially due to demographic change. It has the accelerating demographic change of Georgia and Virginia but that's less noticeable because the state was already so blue.
When it comes to electing "moderate" Republican governors, Maryland is not Massachusetts or Vermont or even New Jersey. Larry Hogie is only the second Republican to win two terms in the history of the state. Of the 40 times the gubernatorial elections have been since the end of the Civil War, Republicans have won the state just seven times. This isn't chest-beating - Hogan will be the last Republican governor for a very long time. Maryland went 35 years between electing Agnew and Angry Bob, and Agnew only won because he broke 70% in MoCo against a segregationist.