I tried the Material Parameter Collections solution, but was not able to get it fully working.
MaterialCollection0.Vectors[i] was available and partly worked, but I did not find any way to access a scalar value. Does anyone have an Idea how to access a scalar in the code for the custom node?
MaterialCollection0.Scalars[i] did not work.
The second problem I encountered was that while it actually worked with Vectors, the input did not update when the MPC value was changed. It just used the value that was set as default in the MPC.
A solution for these 2 problems would be amazing!