If you can’t get the old config file to boot, you should in theory at least be able to decompress the config .tar and see if it contains the pwenc_secret file.
If it does you can extract any existing key from the other file (the .db) using something that reads sqlite3, as shown in this blog:
You may opt to do this on a client computer, in which case you need to adapt the method to read and unencrypt the keys.