I think depending on the officer in question, these roles are filled in different ways. Samantha Wildman was the science officer but not the first officer, because she had no business being one. Spock was first officer and science officer because he could handle both duties, as a super smart Vulcan. T'pol, was in the same vein. Data is capable of being both science officer (probably) and ops manager because he could handle both duties, in the vein of Spock as well. Saru was science officer on the Shenzhou and Michael was the dedicated first officer. They switched roles later on the Discovery. Science officer does not have to equate first officer, nor does a ship being a science vessel demand that the first officer be science officer, I would assume. For the most part, science officer is just filled in with anyone who knows a little more science than other ppl in Star Trek's storytelling, given that Seven, for all intents and purposes, is basically the science officer after Samantha disappears from the show.
Tuvok was once a science officer, but later became a security/tactical officer. He probably could have been security/science or tactical/science if tactical and security were split positions (in the Titan books, security/tactical are in split between two people IIRC, one of them being Tuvok) and still wear gold.
Tuvok was once a science officer, but later became a security/tactical officer. He probably could have been security/science or tactical/science if tactical and security were split positions (in the Titan books, security/tactical are in split between two people IIRC, one of them being Tuvok) and still wear gold.