Legacy Battlenet accounts were purged years ago.
The store, launcher, and account management will all direct to the the only official current version, Reforged.
If you want to play the pre-Reforged version(s), you have to go find them on the internet. The only exception is 1.27 is available from Bliz.
The only restriction is you can’t connect to Battlenet or it will upgrade to Reforged.