Back in January 2023 I created a Private/Public keys paper wallet with an Wallet Generator
website that has been copied to a local folder on an offline laptop (security oblige).
Lately (Jan 2024) I used this Paper Wallet to purchase a little bit of Bitcoin from a vendor machine.
I was eager to import the private key into an updated Bitcoin Core V25, as I’ve done this many times in the past for others, and myself.
The import procedure went smoothly.
Later, I encountered some issues with my Linux PC HDD and decided to scrap the whole
installation and re-installed Bitcoin Core (this time Version 26) with a freshly downloaded complete blockchain .
I was surprised to find out that I could no longer import my private key,
as I was getting the exact same error as digital_mine, OP.

Suffice to say, after reading this whole subject, I was quite surprised because just about 1 month ago,
I was successfully importing my private key without any issues, with Version 25.
After encountering this problem and read this whole post, I figured,
“let just install a previous version of Bitcoin Core, say V23” just to load my private key, as
I just did a month ago with V25. Nope! Didn’t work! Same error message.
The Questions:
Why did it work fine, last month ?
What was done such that I was able to load my private key ?