> They're also hesitant to ping coworkers and ask for screen sharing time because they can't sense if the more senior developers are working on something.

My team's solution is for one developer to just ping another when needed and if they don't reply for a while, they are busy. Don't be afraid to ask, but don't take a lack of a quick reply personally.

With Slack, whether they are currently working on something is not important. If they are busy, the message can just sit there until they have time.