While the answer by Hans Olsson is still technically correct, the Modelica Specification is about to change in that regard, and in fact all major tools seem to support the upcoming specification already, at least if the appropriate options have been set.

Here is the related ticket
https://github.com/modelica/ModelicaSpecification/issues/3489

And
here the upcoming specification
https://specification.modelica.org/master/MLS.pdf (Section 4.4.5 now reads:

"If the Boolean expression is false, the component (including its modifier) is removed from the flattened DAE, and connections to/from the component are removed. Such a component can only be modified, used in connections, and/or used in a modifier of another conditional component with a false condition. There are no restrictions on the component if the Boolean expression is true.")