The error you encountered can happen if the path is incorrect or if the block does not support the operation you're attempting.
In Simulink, the path to a block should be specified using the full hierarchical path from the model root. For example, if your FMU block is inside a subsystem, you need to include the subsystem name in the path.
You can try doing something like this to retrieve or modify the visibility parameter of the ports within an FMU block:
% Correct path to the FMU block
fmu_block_path = 'MyModel/MyFMU';
% Retrieve all parameters of the FMU block
fmu_params = get_param(fmu_block_path, 'ObjectParameters');
%This will display a list of all parameters associated with the FMU block. Look for parameters related to the visibility of ports and variables.
% Assuming 'OutputPortVisibility' is a parameter for controlling visibility
current_visibility = get_param(fmu_block_path, 'OutputPortVisibility');
disp(current_visibility);
Hope it helps!
