Default folder for PuTTY (Windows) to pickup the private key

Solution 1:

After selecting the key file, go back to the first page; select "Default Session"; then click "Save". Everything that you've configured (key path, username, port...) will be saved as defaults.

If a key was saved to "Default Session", it'll be used when you run putty [email protected]. If instead you saved it to a custom session, putty -load MySession [email protected] will use that.

Alternatively, load the .ppk file into Pageant (which is PuTTY's equivalent of ssh-agent), by double-clicking it or dropping it into the shell:startup folder. All keys loaded into Pageant will be automatically used by PuTTY and WinSCP no matter which session you load.

Windows also comes with OpenSSH – the ssh command – which has its own configuration in the ~/.ssh/config file and its own ssh-agent where you can load keys via ssh-add (and remembers the loaded keys across reboots, unlike the Linux version), but by default it will look for private keys at ~/.ssh/id_rsa plus a few other similar names (id_ed25519, id_ecdsa, etc.)