On the Budget > Budget view & Settings view, I can click on any table header like Inflow, Outflow (for alphabetical category sorting), Expected, Budgeted, Activity... to sort by ascending/descending value.

However I cannot revert to the original sorting, by category order (the same in the Setup > Categories definition).

I see an empty space on the left of Inflow/Outlow (and also one to the right of the headers), this seems like a good place to put a revert button (typically a counter-clockwise circle arrow) with a hover tooltip "Revert to default category order".