I see you kept insisting about the ground in this thread.
Here is a link to online NFL rule book
https://operations.nfl.com/the-rules/nfl-video-rulebook/fumbling-in-the-end-zone/
and here is relevant excerpt about what a fumble is :
“A fumble is any act, other than a pass or kick, which results in a loss of player possession.”
Amazing that it does not mention ground anywhere....