28 November 2020 - just upgraded to 'Big Sur' and there it is! Apple Mail is back on form, with functional, sizeable, movable columns. It has instantly elevated Apple Mail back to its previous state of usefulness and value. Apple Mail is once again a valuable mail program. Thank you Apple for listening and reversing your decision.
My final hope is that Apple will learn from this disaster. We have witnessed one year of not listening to massive numbers of dissatisfied customers, a complete refusal to engage in dialogue and the adopting a stand-off position which intensified frustration and rage. Never admitting that a mistake was made or that there was an intention to correct the error.
So, finally and in summary (1) Thank you Apple for restoring Apple Mail to the great program it was before Catalina, and (2) Please reflect and change on how you received, learn from and implement customer feedback - as without us -- your customers -- you will fail as a company.