Why my If node doesn't work only if I change the value of Desaturation in PostProcess Material?

[30.notmeagain]

I am trying to change value of Desaturation in my Black and White Shader with excluded objects from this tutorial (https://www.youtube.com/watch?v=nrN4LxY_J7k&t=442s).

As you can see on the first picture everything is fine with no link to “Fraction” pin. When I add parameter that defines desaturation level it shows me an Error. Is there a way I can fix this problem? I need this asap for my school project.
![Screenshot 2024-01-17 191729|690x381]

[30.notmeagain]

I solved it myself, but maybe it will be helpful for someone so I will post the answer here. I used Lerp function. This function interpolates saturated and desaturated textures based on “Alpha” pin (my ‘DesaturationValue’ Parameter).