The issue is that I want to use a wallet created with segwit/taproot compatible versions of bitcoind in the old version of clients.
All wallets created with new software are incompatible with older versions.
You cannot use a wallet created with the latest bitcoind in an older version of bitcoind!
Impossible!
Go get a copy of Microsoft Office 2021 create a word document then install a copy of office 2003 and try to open that doc. It wont.
Its the way software has worked since forever, older versions of applications cannot always open files created with never versions.
You could probably tweak the code a bit and compile it that it will open it, but you can't be sure that something else isn't going to cause an issue.
-Dave