Recently, Apple launched a new feature on Apple Music called Karaoke Mode, which adds a Sing feature where the lyrics on select (supposedly tens of millions) of songs. I noticed that a ton of the Pixar music with lyrics (though not everything) supports Apple Music Sing. There are some songs where you can still here the lyrics but on many songs it does a very good job of effectively releasing an instrumental track since Pixar has released official instrumental tracks to their lyrical music very rarely. Note that an Apple Music subscription is required to access this feature - unfortunately, I don't believe it works on music you own digitally if you aren't subscribed.
I've gone through all the soundtracks and the list below is all the songs from Pixar soundtracks I can find that support the feature. Note that films whose soundtracks do not contain any songs with lyrics, and who do have songs with lyrics but none support Apple Music Sing, are omitted from the list below.
Toy Story
"You've Got a Friend In Me" - Randy Newman
"Strange Things" - Randy Newman (oddly it doesn't support Apple Music Sing on the Legacy Collection album from 2015, only the original soundtrack from 1995)
"You've Got a Friend In Me (Duet Version)" - Randy Newman & Lyle Lovett
A Bug's Life
"The Time of Your Life" - Randy Newman
Monsters, Inc.
"If I Didn't Have You" - Billy Crystal & John Goodman
Cars
"Real Gone" - Sheryl Crow
"Life Is a Highway" - Rascal Flatts
"Behind the Clouds" - Brad Paisley
"Our Town" - James Taylor
"Route 66" - John Mayer
"Find Yourself" - Brad Paisley
WALL-E
"Down to Earth" - Peter Gabriel ft. The Soweto Gospel Choir
Toy Story 3
"We Belong Together" - Randy Newman
"You've Got a Friend In Me (Para el Buzz Español)" - Gipsy Kings ft. Nicolas Reyes & Tonino Baliardo
Cars 2
"You Might Think" - Weezer
"Collision of Worlds" - Brad Paisley & Robbie Williams
"Mon Coeur Fait Vroum (My Heart Goes Vroom)" - Bénebar
"Polyrhythm" - Perfume
Brave
"Touch the Sky" - Julie Fowlis
"Into the Open Air" - Julie Fowlis
"Learn Me Right" - Birdy & Mumford & Sons
Cars 3
"Run That Race" - Dan Auerbach
"Kings Highway" - James Bay
"Glory Days" - Andra Day
"Ride" - ZZ Ward ft. Gary Clark Jr.
"Drive My Car" - Jorge Blanco
"Freeway of Love" - Lea DeLaria
Coco
"Everyone Knows Juanita" - Gael García Bernal
"Un Poco Loco" - Anthony Gonzalez & Gael García Bernal
"Remember Me (Lullaby)" - Gael García Bernal, Gabriella Flores & Libertad García Fonzi
"Remember Me (Dúo)" - Miguel ft. Natalia Lafourcade
Latin American Bonus Tracks (in italics)
"Recuérdame" - Carlos Rivera
"El corrido de Miguel" - Bronco
"La Bikina" - Karol Sevilla
"Bésame Mucho" - Jorge Blanco
"Un Mundo Raro" - La Santa Cecilia
"Recuérdame (Solo" - Natalia Lafourcade
Incredibles 2
"Here Comes Elastigirl - Elastigirl's Theme (A Cappella)" - DCappella
"Chill or Be Chilled - Frozone's Theme (A Cappella)" - DCappella
"The Glory Days (A Cappella)" - DCappella
Toy Story 4
"You've Got a Friend in Me" - Randy Newman
"I Can't Let You Throw Yourself Away" - Randy Newman
"The Ballad of the Lonesome Cowboy" - Chris Stapleton
"The Ballad of the Lonesome Cowboy (Soundtrack Version)" - Randy Newman
Onward
"Carried Me With You" - Brandi Carlile
Soul
"Rappin' Ced" - Daveed Diggs
"It's All Right" - Jon Batiste
International Bonus Tracks (in italics)
"It's All Right (Duet Version)" - Jon Batiste ft. Celeste
"Escucha la vida" - Pablo López
"Je reviens plus fort" - Abi Bernadoth
Turning Red
"Nobody Like U" - 4*TOWN (From Disney and Pixar's Turning Red), Jordan Fisher, Finneas O'Connell, Josh Levi, Topher Ngo & Grayson Villanueva
"1 True Love" - 4*TOWN (From Disney and Pixar's Turning Red), Jordan Fisher, Finneas O'Connell, Josh Levi, Topher Ngo & Grayson Villanueva
"U Know What's Up" - 4*TOWN (From Disney and Pixar's Turning Red), Jordan Fisher, Finneas O'Connell, Josh Levi, Topher Ngo & Grayson Villanueva
"U Know What's Up (The Panda Hustle Version)" - 4*TOWN (From Disney and Pixar's Turning Red), Jordan Fisher, Finneas O'Connell, Josh Levi, Topher Ngo & Grayson Villanueva
"Pandas Unite / Nobody Like U (Reprise) - Ludwig Göransson, 4*TOWN (From Disney and Pixar's Turning Red), Jordan Fisher, Finneas O'Connell, Josh Levi, Topher Ngo & Grayson Villanueva
I'm also including a few titles not made by Pixar but canon to Pixar-created franchises in case anyone is wondering about them.
Planes
"Nothing Can Stop Me Now" - Mark Holman
"You Don't Stop - NYC" - Chris Classic & Alana D
"Fly" - Jon Stevens
"Love Machine" - Carlos Alazraqui & Antonio Sol
Planes: Fire & Rescue
"Still I Fly" - Spencer Lee
Monsters at Work
"Don't Stop Now" - Dominic Lewis
"End of the Line" - Dominic Lewis
"World on Fire" - Dominic Lewis