There's no backwards compatibility with any scenery or aircraft from existing cobtent by third-party creators.
I have Megascenery for flight Sim X that won't be usable in FS 2020.
It does look nice though! I'm weary how good it's going to be since there's a big Xbox logo. I'm aware that it is their all encompassing brand for gaming content now, but I'm still weary.
If you were born after December 31st 1964, you weren't a Boomer.
You never see them go. They're always full. No one ever gets on, but they're always...they're always departing, but they never arrive...and the ones that do arrive, they never leave.