Base64 wallet decoding in 2014

There is a Bitcoin wallet file (not wallet.dat). I have a string like this:

FuXjd1EjroiAURK…5zYDsaaP/1FizzJo0IrkwEe6bmN7av0ww==

I omitted the middle part (…). 728 characters It was long, and it was. Created in July 2014. I don’t remember what I made.

I tried this: Convert Base64 Private Key to WIF (both answers), but I didn’t get the address in any transaction. The way the file was saved leads me to believe it was used.

Since it is from 2014, it does not seem to be an HD wallet and most of the BIPs have not been developed yet.

How can I decipher this?