I have the same problem/question as the OP. But his solution doesn't work for me.
To be honest, I wasn't even aware about the old behavior the OP refereed to because I'm new to this program. But I was watching the tutorial video where they simply dragged the folder into ST and it automatically opened the side bar. In my case, it doesn't happen, so I always have to go with Ctrl+K, Ctrl+B to open it. The only relevant difference between my setup and the one form the tutorial that I can think of is that they were using Mac and I'm on PC. Could that be the factor here?
Also, the program is in a clean state. No single package has been installed so far.