So, apparently QuickBooks changed something YET AGAIN that had no business being changed.
Why can I no longer choose period comparisons? Your "comparison" report is useless. There is nowhere to customize. There is not "dropdown" for the report period, it's simply an information link, no dropdown. The dropdown is for the current period only, not comparison. When you click "Customize" there is nowhere to include a previous period.
So, QuickBooks, where do I find the period comparison reports? Because whatever new "comparison" report you included isn't correct.