This doesnt work well with PrntScrn generated screenshot window. You have to combine the keys in this order instead:
- Right click the top window bar
- Choose window
- Unmaximize
- Repeat step 1 and 2
- Select Move with Keyboard (Resize with keyboard does not work)
- Press Keyboard arrow up to shift the whole window upwards to show the "save" button. ( Unfortunately you end up loosing access to the top window bar: but at least you can now save your screenshot)