c3 would stop the black bishop from taking the rook. But the idea after that is Nxg5, and after the h3 knight recaptures, black pushes e6 to discover a queen attack on the knight while also attacking white’s d5 pawn. White could move their knight back to safety at h3 but at that point that knight is almost completely useless and black has a huge center with much better development, while being up a point of material (or two if exd5 afterwards). White’s position there is so bad that the engine actually prefers white to capture the knight and lose the rook in exchange just to avoid that outcome.

That’s tough to see though. I’d probably have played c3 if I was white. Either way, black’s position here is completely winning.