This is a suggestion to enable undoing even after a project has been closed and re-opened later.
Why? Because s*** happens and also it is more in the spirit of ‘non-destructive’ editing.
Real world case that happened: my son lost all the work he was doing on a project because (I think) he accidentally opened a video file with “open file” and probably did an overwrite of the whole edited track, then must have saved. This is a bit of an extreme case of course, but these kinds of errors do happen.
In a more normal workflow you might do some edit / cut or modification close Shotcut and then when reopening may want to go back.
For instance Ardour has this feature and saves the undo history, so when you re-open a session you can still undo stuff which was done previously.