A better synonym would be “to be precise”. Antonym: “generally speaking” which could express opinion or point of view. Hope this helps.

In this sentence, "strictly speaking" means "precisely" or "in the most exact terms." It's used to clarify that the statement being made is accurate based on formal or technical definitions. It doesn't mean "actually" in a casual sense but rather emphasizes being exact and not deviating from the precise meaning.