The engine evaluation on lichess goes up to +5 at different times, or up to +20 depending on your engine, but once the white pawn in on g6, how does White win - either via a simplification to a tablebase position, or a clear step-by step a plan that can be described in words?
Can the white king ever march to the queenside without losing the h4 pawn? Or maybe h4 pawn can be given up?
If not, was the win achievable earlier in the endgame?
My own analysis goes like this, but I am far from being convinced, thus this post. The basic idea is that White tries to give up h4 pawn, but black delays/refuses to take it so as not to expose h5 pawn, which is the strangest thing I've seen, and if White wins h5 pawn (via zugzwangs), the doubled g5 pawn defends White king on h5 against checks, so White gives checkmate with g6 pawn, which is another twist...
[Event "World Rapid Championship"]
[Site "Moscow RUS"]
[Date "2019.12.28"]
[Round "13.4"]
[White "Korobov, Anton"]
[Black "Nepomniachtchi, Ian"]
[Result "1/2-1/2"]
[ECO "D73"]
[WhiteElo "2668"]
[BlackElo "2767"]
[Annotator ""]
[PlyCount "152"]
[EventDate "2019.12.26"]
1. d4 Nf6 2. c4 g6 3. g3 c6 4. Bg2 d5 5. cxd5 cxd5 6. Nc3 Bg7 7. Nf3 Ne4 8. O-O
Nxc3 9. bxc3 Nc6 10. Nd2 O-O 11. e4 dxe4 12. Nxe4 b6 13. Bg5 h6 14. Bf4 Bb7 15.
Re1 Rc8 16. h4 Na5 17. Qe2 Qd7 18. Rad1 Bd5 19. Nd6 exd6 20. Bxd5 Rxc3 21. Qe4
Qg4 22. Rc1 Rxc1 23. Rxc1 b5 24. Rc7 Qd1+ 25. Kg2 Qxd4 26. Qxd4 Bxd4 27. Bxd6
Bb6 28. Rd7 Rd8 29. Bxf7+ Kh7 30. Rxd8 Bxd8 31. Bc5 a6 32. Bd5 Bf6 33. Kf3 Kg7
34. Ke4 Nc4 35. Bb7 Nb2 36. Bb4 Na4 37. Bxa6 Nc3+ 38. Bxc3 Bxc3 39. Bxb5 Be1
40. Ke3 h5 41. a4 Kf6 42. Ke2 Ba5 43. Bd3 Bb6 44. Kf3 Ba5 45. Kg2 Bb6 46. f3
Kg7 47. g4 Ba5 48. g5 Be1 49. f4 Kf7 50. Bc4+ Kg7 51. Kh3 Kf8 52. f5 Kg7 53.
Bb5 Kf7 54. fxg6+ Kg7 55. Bd3 Ba5 56. Kg2 Bb4 57. Kf3 Be1 58. Bf5 Ba5 59. Bd3
Be1 60. Be4 Bd2 61. Ke2 Ba5 62. Bf3 $4 (62. Ke3 Be1 63. Kf4 Bxh4 {this exposes
h5 pawn paradoxically} (63... Ba5 {Black can try to resist taking on h4, but
White forces it by threatening to go to queenside} 64. Ke5 Be1 65. Kd4 Bf2+ $2
66. Kc4 (66. Kd3 $3 {only move, king goes back while covering e3 square} Be1 (
66... Kg8) (66... Bxh4 67. a5 $18 {Black has no time to take on g5 here} Bxg5
68. a6 $18) 67. Ke2 Ba5 68. Kf2 Bc3 69. Kf3 Ba5 70. Ke2 Bb4) 66... Bxh4 67. a5
Bxg5 $3 $11 (67... Bf2 $2 68. Kd3 $1 {king goes back!} Bg1 69. Ke2 h4 70. Kf1
Bc5 71. Kg2 Ba7 72. Kh3 Bf2 73. Kg4 Kg8 74. a6 Kg7 75. Bf5 {ZUGZWANG} Kg8 76.
Be4 Kg7 77. Bd3 (77. Kh5 $4 h3 $11) 77... Kg8 78. Kh5 $1 (78. Kf3 Bd4 79. Kg4
Bf2 80. Kh5 h3 81. Kh6 {and g5 pawn allows White to win.} h2 82. Bc4+ Kf8 83.
g7+ Ke7 84. Bd5 $18) 78... Kg7 (78... h3 79. Kh6 h2 80. Bc4+ Kf8 81. g7+ Ke7
82. Bd5 $18) 79. Bf5 $1 {ZugZwang})) 64. a5 Bf2 65. a6 Kg8 66. Kf3 Bg1 67. Kg3
Be3 68. Kh4 {and White wins the h5 pawn first, then goes off to the queenside
to win the bishop.}) 62... Kxg6 63. Bc6 Kf7 64. Bf3 Kg6 65. Bc6 Kf7 66. Bb5 Bb4
67. Kf3 Be1 68. Be2 Kg6 69. Bd3+ Kg7 70. Bf5 Ba5 71. Bg4 Kg6 72. Bxh5+ Kxh5 73.
Kf4 Be1 74. Kf5 Bxh4 75. g6 Kh6 76. a5 Kg7 1/2-1/2