Accessory maker MobaPad says that Switch 2 will accept Switch cartridges and extra Joy-Con buttons - eviltoast
Report suggests Switch 2 can play all original Switch games
arstechnica.com
New Joy-con buttons, 1080p screen also feature in MobaPad's "first-hand information."

MobaPad is a Switch controller and game case maker (that I have never heard of), so they should have reliable info. They said that:

  • The Switch 2 will have physical cartridges and the slot will also be able to accept Switch 1 games.
  • There will be a new button on the back of each Joy-Con, behind the triggers.
  • There will be a new button on the right Joy-Con, by the Home button.