Let's start with an essential point.  There's a pretty good argument that every ride at the Magic Kingdom is a must-ride.

It's called nostalgia.  Call it "magic".  Every ride has something.

I wouldn't tell you to stay away from Peoplemover because it's boring or to avoid Space Mountain

 There's no denying that Magic Kingdom is a titan of a theme park.  

 If you can find a way to experience everything, do it.

1. Seven Dwarfs Mine Train

1. Haunted Mansion

3. Big Thunder Mountain Railroad

4. Splash Mountain (closed permanently beginning January 23, 2023)

5. Tomorrowland Transit Authority PeopleMover

6. Jungle Cruise, Pirates of the Caribbean and many more