Simulink.Parameter is used to define the port dimension of a signal. Symbolic dimensions appear as compile time macros in the code, e.g. my_vector [my_dim], when my_dim is defined as a compiler flag or macro. Therefore, they have to be associated with a Storage Class that generates such constants in the code, and the error message is clear what Storage Classes need to be used. See following doc for more details:
If you do not want your size to be compile time tunable, then disable "symbolic dimension propagation" as the error message suggests.
