Have you ever seen the late-1940s biopic of Jerome Kern, titled "Til The Clouds Roll By"? My wife found it on Netflix or Amazon recently and it was pretty good. It starts with a 20-minute condensed production of Show Boat and then flashes back to Kern's beginnings as a songwriter. The biopic part was a bit flat, but the production numbers sprinkled throughout make up for it. Lots of big-name performers appeared in it - never thought I'd ever see Sinatra singing "Ol' Man River".
Yes, I’ve seen it. I think it’s with Robert Walker? And yes, it does have a young Frank singing Ole Man River. I have it on one of my Sinatra records.
Those 40s musical biopics were not my favorite except for Yankee Doodle Dandy.