When I first set up 2FA on the Mac it was with Google Authenticator 2FA to open the wallet.

I cannot remember every step I took to set up this original Mac wallet but I stored pertinent info, just in case... eg seed (plus extension), master public key

I had made a previous successful transfer of BTC from Linux to Mac to check it was all working. It was, there came up in the Mac wallet automatically the transaction to counter sign. I had not even been made aware then of the use of loading a saved transaction as I hadn't needed it.

I subsequently send before the first BTc fork funds to the Linux wallet and just recently returned to the Linux wallet to move them to the Mac wallet and encountered this problem. I think I have gone to the new version in this time.