(UPDATE: September 1, 2020) Here's a list of films available to stream that are part of the Warner Bros. library (Warner Bros./MGM/RKO).
For all films featured on HBO Max's TCM channel: HBO Max | TCM
For a list of Looney Tunes shorts: HBO Max | Looney Tunes
For a list of Popeye shorts: HBO Max | Popeye
For a complete listing of available HBO Max titles: HBO Max | Complete Collection