FIFY
Altimeter setting easily changes even over a 1 hour flight. I’ll take off from Nashua, and by the time I get north of Manchester it could easily be different. It could even be different between Manchester and Concord which is a 15 minute flight. That’s why every time you talk to a new controller they tell you the pressure, and one reason it’s so important to listen to ATIS before you arrive at your airport.
I’m not seeing much of anything different in MSFS that I see in real life, other than the suddeness of the change.