If you’re just getting into flight sims, I’d definitely start with Stick and Rudder — it may be old, but it explains the “why” of flying better than most modern books. Then move on to something like The Pilot’s Manual: Ground School for more structure.
For MSFS and DCS, YouTube is gold — FlightChops, Captain Joe, and Grim Reapers make learning fun and practical. You’ll pick up a lot faster when you combine reading with actual in-sim practice.