For bitcoin there is Bitcoin Core which downloads the whole blockchain a few hundred gigabytes then you can use the wallet.

For Ethereum, there used to be a wallet. I have done a backup of the key stores but now I am trying to download that classic wallet but I can't find a download link.

The only nearest thing I found was MyEtherWallet (MEW) but then there is no Download button anywhere on their website, and even whien i try the software version it says Not recommended:
https://www.myetherwallet.com/access-my-wallet

Any help how to get access to a wallet using the backup keystores from the "old"/"classic" wallet?