In your untitled-1.nb near the bottom, Cb appears to be a function from your ParametricNDSolve, but then it looks like you use Cb as an independent variable {Cb, 0, 100} inside your Manipulate.

Look at this ParametricFunctionDocumentation and use your Cb in exactly the same way that page uses pfun and see if you can get your problem fixed.

In your 2.nb near the bottom Ca appears to be a function from your ParametricNDSolve, but if you look inside that you see it is Cb[ t ] and not Cb[ Km ] [ t ] . Again look at the documentation and try to understand exactly how to use functions.

I understand that Mathematica notation can often be very confusing and it can be very difficult to understand what the problem is or how to solve it. Studying how functions are defined and used, how Interpolating functions are defined and used and now how ParametricFunctions are defined and used will save you many hours of pain and suffering and needing to ask again and again and again "I typed some stuff in and it doesn't work. Please fix it."

oops .... to many {km} at the end of model1. This is the correct version:

Model1 = ParametricNDSolve[{ Ca'[t] == ((Vmax Cb[t])/(Km + Cb[t]) - Pdiff Fuc Ca[t] + Pdiff Cb[t])/Va, Cb'[t] == (Pdiff Fuc Ca[t] - Pdiff Cb[t] - (Vmax Cb[t])/(Km + Cb[t]))/Vb, Ca[0] == 0, Cb[0] == Cb0 }, {Ca, Cb}, {t, 0, 100}, {Km}, PrecisionGoal -> Infinity]