The spacebar trick allows the original name to be restored, but it doesn't allow stacking with similar items.
I tested with a book. Steps:
Take one of a stack
rename to something custom
Use space character " " to remove custom name
Expected results:
Renamed book can be stacked with items as before
Actual results:
Renamed book can not be stacked with items
I'm still seeing this behavior in 1.16.2