Gilmoy: <26.Nd7> is actually a live OTB <Plachutta> interference! We have two lines-of-protection by two line-movers of the same type:
(1) Qd8 protects Bd6
(2) Re7 protects Rc7
* also, Rc7 is pinned to White's Rc8 threat
The Plachutta comprises 2 deflection-sacs <26.Nd7 27.Bxd6> to lure + deflect the Re7, unprotecting the Rc7. Unlike a composed problem, here it wins material instead of forcing a mate.
Black actually looks deep enough and chooses the game line as the least-costly solution.
A. 26..Rcxd7 27.Bxd6 drops at least an exchange for White after the Rd7 sits, goes back to Rc7 (to block c8), or Black blocks with Re6. 27..Rxd6 28.Rc8 drops Q for R, which is worse.
B. 26..N(either)xd7 drops a full Rook after 27.Rxc7 Bxc7 28.Rxe7 Qxe7 29.Rxc7.
C. <26..Rexd7 27.Bxd6 Rxc2> wins N+BR for BR, and then <29.Rc8 Qxc8> returns Q for R, resulting in a net trade of RN(+RB) for Q(+RB), nearly equal and worth fighting out.
Mnemonic: Ba3, Bh3, PlaBh3tta!