Can a 1D LUT be used in ffmpeg using lutrgb?
The LUT filters don't have cross-referencing of channels. Use geq instead

geq=r='if(gt(g(X,Y),145),255,p(X,Y))':g='if(gt(g(X,Y),145),255,p(X,Y))':b='if(gt(g(X,Y),145),255,p(X,Y))'