In the episode "Good, Bad Boy" there was a biracial couple dancing. They were in the forefront of the dance floor during a reform school dance. It first shown on February 11, 1972

I don't know. I guess the places to hunt would be Room 222 and The Bill Cosby Show?

The Partridge Family, "A Man Called Snake," 1971, has a dance scene, but I think it's all intraracial. There's even one black guy dancing by himself in the middle of the floor.

There was an interracial kiss in a 1968 episode of the original Star Trek series.

Room 222, December, 1970. The dance starts around 17:00:

https://youtu.be/e49wNvzeDRE?si=VZNgNwWZ2Q3RYPUq

Bill Cosby Show, January 1970. Dance starts around 16:45:

https://youtu.be/6iMFUjSy3FE?si=vzv4Pot9T9xe1x0S

Hard to tell who is dancing with who.