Hi There,
Welcome to the Method Forums!
The Grids in Method New are not able to be set as 'Editable' on the Grid object itself as it was in Classic. There were a few design/aethetic reasons for this, but we wanted to make the addition of items or records a little more robust overall (hence the new screens when adding Grid items in the stock Apps)
This is certainly something we are taking into consideration adding at a future date, and I'll be sure to bring up your feedback with the team!.
If you have any other platform suggestions, please let me know! Definitely happy to take any and all feedback :)
Regards,
-Ben