When Michael R. Jackson’s debut musical “A Strange Loop” premiered off-Broadway at Playwrights Horizons in 2019, it was an immediate sensation. A musical about a Black gay man writing a musical about a Black gay man, the show combines captivating metafiction with hilarious pop culture commentary, bawdy sexuality and deeply touching doubts and introspection. Usher, an usher for “The Lion King,” is plagued by nagging Thoughts that take on the roles of his parents and others in barraging him with pretty much every insecurity he has. Now making its West Coast premiere at American Conservatory Theater, “A Strange Loop” won...