It's the guy you don't see listed on the main "cast" page, and is down at bottom, uncredited with anything in particular, of the extended cast page: Hal Willner.
This recording was a Hal Willner joint. You need to go outside of IMDB. Start with his wikipedia page. His specialty over 40 years (apart from driving SNL's music) was "tributes" - a name that doesn't do the albums of contemporary musicians covering important composers justice. Monk. Mingus. Weill. Rota. Every one of them is absolutely amazing, and a product of Willner's choice of musicians to bring into each. So when you look down this list and see Bill Frisell and Wayne Kramer listed as "session musicians" (which they really aren't), it conveys nothing of the unique musical character each one bring.
This was particularly touching given that Willner was killed by COVID early in the pandemic (he got one of those RIP closing credits on that week's SNL), and it took a few more years for this documentary - as much of the making of the album as about Bolan himself - to come out.
You really don't want to miss this one.