This minor 'cosmetic' problem exists in Krita 4.0.0 appimage but was also in 3.3.3.
It has no effect on functionality.

The Edit -> Undo menu statement (and Redo) have problems with stating what they will do.
This can be demonstrated as follows:

Start krita and make a New image. Paint two brushstrokes.

Edit menu shows the 'Undo' option, click this to undo the last brushstroke.
Edit menu will now show the 'Undo Freehand Brushstroke' option for the first brushstroke.
Click this to undo the first brushstroke.

The Undo option should have shown as 'Undo Freehand Brushstroke' on first use.

Do Edit -> Redo to redraw the first bushstroke, it just says 'Redo'.
Edit -> Redo option now shows as 'Redo Freehand Brushstroke'.
Click this to redo the second brushstroke.

The Redo option should have shown as 'Redo Freehand Brushstroke' after the first use of Undo.

Now Add a paint layer and draw two brush strokes on it. Undo is back to saying just 'Undo'.

Undo both brushstrokes and add another paint layer, then do two brushstrokes on it.

Undo now says 'Undo Add Layer' when it should say 'Undo Freehand Brushstroke".
However, clicking Undo will correctly undo the last brushstroke.

The Undo History docker is always accurate throughout this process and the Undo action is always to undo the last action performed.

It seems that the Undo menu option has problems keeping track of the required menu statement.
Redo also has problems with its menu statement but always performs the correct redo action.

The mitigation is to ignore what the Undo/Redo items say and just press them and rely on them working as they should.