I had a backup of my wallet.dat a few years ago, which was encrypted for sure.
But when I try to reload it now, it shows 0 balance and no historical transactions after the whole blockchain sync, and it is weird that the option of encrypt wallet is available.
It sounds like you created this backup before you encrypted the wallet. When you encrypt it, it creates new private keys. If it was funded before you encrypted it, those keys would still be in there. But if you only funded the wallet after you encrypted it, the backup you made before you encrypted it became useless.
I am not so sure about it. But that reminds me something, thank you.
If you still have access to the drive where the original wallet was created, you can still be able to recover it even if it was deleted from that drive.
I don't know what command you use in Pywallet if it's just dump, then try other commands to retrieve these private keys.
Check the links from the quoted below
The original drive was a corrupted SSD which is in a data recovery process,
and it probably won't work because it has been 6 years, I was told there were many electron dislocation on the nands.