Apparent cause: cancer.

https://variety.com/2021/tv/news/willie-garson-dead-dies-sex-and-the-city-white-collar-actor-1235070748/

Excerpt:

....Born William Garson Paszamant in Highland Park, N.J., Garson studied theater at Wesleyan University and received a master of fine arts from Yale Drama School. After graduating, Garson began to book small roles on some of the most popular television programs of the day, including “Cheers” (1982), “Family Ties” (1982) and “L.A. Law” (1986). His other early television appearances included “Boy Meets World,” “The X-Files,” “Friends,” “Twin Peaks,” “Melrose Place,” “Buffy the Vampire Slayer” and “Ally McBeal.” More recently, Garson has held roles on “Two and a Half Men,” “Hot in Cleveland,” “Stargate SG-1” and “Pushing Daisies.” He also dipped his toes in directing, having helmed episodes of “White Collar” and “Girl Meets World” for Disney Channel, in which he also guest starred.

Garson was also a persistent force in film, having worked with directors Peter and Bobby Farrelly on “KingPin” (1996), “There’s Something About Mary” (1998) and “Fever Pitch” (2005). His other film credits included “Soapdish” (1991), “Groundhog Day” (1993) and “Being John Malkovich” (1999).

Most recently, Garson lent his voice to “Big Mouth” and had a recurring role on “Supergirl” from 2019 to 2020. Garson’s upcoming projects included “And Just Like That” and the series “Duke of the Valley.”...