Uhh, why? Zoom calls still exist, you know? We can also communicate through writing and ask questions. What matters is the willingness to acquire this knowledge, not the method used
Additionally, taking the time to take the junior down for some table football or a tea and a chat makes them MUCH more comfortable with you and they'll feel MUCH more able to come to you to ask for help or explanation or admit they don't understand something.
Some just confused mumbling, one made an ee sound, one gave a particular kind of sigh.
Regular checkins, pair coding sessions, onboarding roadmaps, careful selection of initial projects, and fostering an open-door culture should all be a part of managing any new employee, whether in person or remote. And when done properly, there is no difference in the ability for employees to transfer knowledge or get onboarded between in office or remote.