By "Top bar crop" I mean the crop tool next to the hand in the bar as per attached fig.
Let's say it's the
Crop Tool in the
Command Bar.

Something strange is going on, today when I tried it the Aspect Ratio option was available but it certainly was not yesterday! Here is a screen with the Aspect Ratio drop down clearly showing. Is the availability dependent upon any other setting I wonder?
On your screenshot I suppose you cut the
Palettes on the right hand side. If the
Essential Tools palette is present there the
Crop tool is constantly displayed with the
Aspect Ratio option menu available.
As a matter of fact, since I don't care for pre-defined default aspect ratios and since I want to be able to crop each pic to taste my first move when I display a folder of newly shot photos is to select them all and choose the
Unconstrained Aspect Ratio. So I won't have to bother about that anymore.
My second move, while they are still all selected, is to make a
Virtual Copy of them all (Cmd + D). I always make corrections on the #2 copy and keep the #1 uncorrected for future reference (I apply a 2 star rating to it to recognize it). It's very handy. In case I am not happy with the settings I did on #2 I can make a fresh one (or several) from #1 and if necessary delete the ones I am not happy with. This operation is absolutely free of charge. It just adds some data in the .dop sidecar file which amount to some kBs only.
Nick