Yeah, he composed all the music and actually won an Oscar for that. Unfortunately, he doesn’t perform on the songs, but the cast does a pretty good job.
There is an outtake of him and Kermit doing a duet on one song though:
https://www.youtube.com/watch?v=aDnTo2S2BrA
Thanks! Hubby didn’t really know which movie I was talking about, but he did remember him winning the Oscar.