Input and Output of FMUs are determined by the FMU file. The "Input/Output" panel here is used to configure bus object names for structured ports only. If there are no structured input/output ports, the panel is blank.
Refer to this post by MathWorks Support Staff for including tunable parameters while exporting a Simulink model as an FMU: https://www.mathworks.com/matlabcentral/answers/468256-how-to-include-tunable-parameters-when-exporting-a-simulink-model-as-a-tool-coupling-fmu-in-r2018b-o