I can't figure out where the frame rate problem is

Hello everyone, when I was making the game, I always let the FPS show up, one day I had a problem with the frame rate, it was a big map, the plants limited my frame rate, although I deleted the plants, but my frame rate did not come back, when I used the independent full screen window, its frame rate was very low, shrink the window, the frame rate became high, when I ran the game in the editor, it also had a low frame rate, I couldn’t get the frame rate problem at all, even if I deleted a lot of grass