Based on the Space Cadet Shift feature. Tap the Shift key on its own, and it behaves like Enter. When held, the Shift functions as normal.
Replace any Shift key in your keymap with
KC_SFTENT (Shift, Enter), and you're done.
||Right Shift when held, Enter when tapped|
As with Space Cadet Shift, this feature may conflict with Command, so it should be disabled in your
COMMAND_ENABLE = no
This feature also uses the same timers as Space Cadet Shift, so using them in tandem may produce strange results.
By default Space Cadet assumes a US ANSI layout, but if you'd like to use a different key for Enter, you can redefine it in your
||The keycode to send when the Shift key is tapped|