Ed Wood (1994) starring Johnny Depp covers the making of several movies by director Ed Wood. Including: Plan 9 From Outer Space (1957), Glen or Glenda (1953). It's the 90's version of The Disaster Artist.
The Aviator (2004) includes a section about the making of Hell's Angles (1930).
Both biopics. There are also biopics of Marilyn Monroe, Grace Kelly, Laurel & Hardy, etc. I wouldn't even know where to begin.
The Emperor's New Groove was suppose to be the next Lion King. They signed on Sting for the project and his wife got the okay to film it's making. Delays, bugrt overruns, and just not getting it to work made the production unworkable. It was salvaged for the movie we have now. Sting's wife showed her documentary at a film festival. Disney did not like her documentary. Disney owns the rights to the documentary. You can only watch it on a pirate ship. Search for the The Sweatbox.
My Best Friend Fiend is about the insane relationship between Warner Herzog and Klaus Kinski. They made a lot of exceptional movies together. This man is a lot. I don't know how anything got made with him.