Thinking back, I believe the mistake was made when generating the wallet. Instead of going offline, the wallet was generated while still connected to the Internet.
No, the mistake was that you used an unknown website for generating your bitcoin wallet and stored your coins there. Don't even trust offline versions of those websites because there was a website that would let you to generate bitcoin address according to the move of your mouse cursor, i.e. you had to move it many times on your screen and this way you would get randomly generated bitcoin address but the actual truth was that even offline, this website already had generated thousands of bitcoin addresses, they have already saved them in their database and when user would generate one pseudorandom bitcoin address from this website in offline mode and would store coins there, website's owner would get a message about it (he was watching absolutely every address) and would wipe out your wallet.
Thanks everyone. As much as it pains me, I will walk away from this and put it down to a very expensive experience.
What about bitaddress.org as a paper wallet generator. This time, of course, I will generate the wallet offline. Is this still asking for trouble or should I stick to hardware like ledger?
The safest and the most secure options among hardware wallets are: The Passport Foundation and Coldcard.
You can use Sparrow or Electrum to generate bitcoin address on your computer. Users above me have already written what you should do.