Aside from the New Songs in Digimon Adventure  (or also called "REBOOT" ) there are some changes made in the anime.
One Notable Factor was that:
The first three episodes of 2020 was basically a movie
they're basically one long prologue to the new series. The end of episode 3 essentially feels like the true beginning to Adventure 2020.
No, it's not. Digimon (not Appmon) in Appmon are explicitly fictional, though an Agumon leaves its video game at one point. Additionally, the Adventure epilogue shows a world where everyone has Digimon, but in Appmon it's a world much like our own.
(Another note: That 'in the year 2045' thing at the beginning of each episode is quoting a certain AI ...