There will be some slight differences in the sound set between MSFS 2020 and MSFS 2024, just by nature of the difference in the sound engines of each simulator, but there shouldn't be any significant differences with regard to engine sound or ground roll. I have just quickly loaded up MSFS 2020 to check this, and the sounds are playing as expected on my.
One thing I would recommend double-checking is that all your Sound Options are set to 100 (full volume) in MSFS 2020, and that you have Active Spatial Sound and Headphone Simulation "OFF". I have attached my Sound Options page for reference.
[image: 75a4dd87-a18a-4595-9a68-f3129a9b5a75.png]
Hope that helps.
Mark - Just Flight