I'm not sure about a world championship game, but genuine underpromotions do occur now and then in grandmaster games.
For a starting shot, here is the famous 2012 game with a knight promotion by Hikaru Nakamura. According to the FIDE rating website, Nakamura's *rating at the time was 2783 the month game was played. By "highest level," I took that to mean the highest rating of a player in a professional game with a genuine underpromotion occurred.
[Title "Hikaru Nakamura-Vladimir Kramnik, Chess Olympiad, Istanbul Turkey, 9/6/19"]
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1. Nf3 Nf6 2. g3 g6 3. Bg2 Bg7 4. c4 c6 5. d4 d5 6. cxd5 cxd5 7. Nc3 Ne4 8. Qb3 Nxc3 9. bxc3 O-O 10. Nd2 e6 11. e4 Nc6 12. O-O Na5 13. Qd1 Qc7 14. Qf3 b6 15. Ba3 Rd8 16. e5 Ba6 17. Rfe1 Rac8 18. Bb4 Bh6 19. Qd1 Nc6 20. Ba3 Na5 21. Bb4 Nc6 22. Ba3 Na5 23. Nb1 b5 24. h4 Nc6 25. Bc5 Qb8 26. Qe2 Na5 27. Nd2 Rxc5 28. dxc5 Qc8 29. Nf3 Qxc5 30. Nh2 Bg7 31. h5 g5 32. h6 Bxh6 33. Qh5 Bg7 34. Qxg5 Nc6 35. Ng4 Qe7 36. Qxe7 Nxe7n37. a4 d4 38. axb5 Bxb5 39. Rxa7 d3 40. Rxe7 d2 41. Rd1 Be2 42. Ne3 Bxe5 43. c4 h5 44. Ra7 h4 45. Ra2 Bxd1 46. Nxd1 hxg3 47. fxg3 Bxg3 48. c5 f5 49. Ra7 e5 50. c6 e4 51. Bh3 Rc8 52. Ra6 Rf8 53. Ra5 f4 54. Kf1 e3 55. Ke2 Rf6 56. Ra8+ Kg7 57. Ra7+ Rf7 58. Rb7 Kf6 59. Kf3 Re7 60. Rxe7 Kxe7 61. c7 e2 62. c8=N+ Kf6 63. Kxe2 Ke5 64. Nb6 Kd4 65. Bg2 Be1 66. Nd5 Ke5 67. Nb4 Bh4 68. Nd3+ Kf5 69. Kxd2 Kg4 70. Ke2 Bf6 71. N1f2+ Kg3 72. Bf3 Bd8 73. Ne4+ Kh4 74. Ne5 Bc7 75. Ng6+ Kh3 76. Ne7 Bd8 77. Nf5 Bb6 78. Kf1 Kh2 79. Bg4 f3 80. Nh4