All destinations are open to all players regardless of expansions owned. It has been this way since Bungie released New Light over a year ago. And by destinations I mean the patrol spaces on all the planets. If you don't own Forsaken then you wouldn't have access to the Forsaken raids and certain Forsaken-locked exotics. Same for Shadowkeep. But in terms of being able to visit the planets either in free roam or as part of a Beyond Light quest (assuming they own BL), yes, any player would be able to do that without owning Forsaken or SK.