The General formatting option is treated by Excel as a sort of "no formatting" option, so it will often try to guess what specific format you want it in.You can enter anything
If the cell is formatted as text before entering, anything you enter is considered text, even numbers
So a formula becomes text and therefore will just sit there waiting.

As first the cell must be formatted ( General is default) then edited, followed by Enter, we did it the same way.
Change format , edit the cell ( F2 does that) then enter

(BTW F2 edits almost everything in MS applications)

Why your cell was formatted as Text, I have no idea

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