There are still “plus” and “minus” keybindings which you can use to interact with various things, but it’s mainly radio frequencies and it works poorly for that to boot (I had trouble switching between wholes and fractions).
In practice, the main options are:
Buy a piece of replica hardware, as the OEMs tend to handle the interfacing with the sim. Except for the Logitech radio panel, this is expensive.
Buy a piece of interfacing software like Axis and Ohs or Spad.next (or FUSIPC?). These allow you to access much wider range of commands, such as G1000 and GNS530/430 keybindings and they can also be used to script custom aircraft specific commands (e.g. scripting a button for door to close).
I suppose you could also wait for Asobo to do something, but last I heard their plan for G1000 command support is “not planned”.