Convert Kleopatra Secret Key to WinSCP .ppk format

Hi,
I would appreciate some help on this matter please. I'm struggling to convert the Secret Keys generated by Kleopatra as Private Key in WinSCP. When I used conversion in PuTTYgen, there is error 'Couldn't load private key (file does not begin with OpenSSH key header)'. Please if you can advise any other alternative for this conversion? I need the PPK to connect to external party where public key already been shared with them.
I'd be grateful if you can advise as Im at a loss at the moment.

Many thanks.

sorry, I do not know Kleopatra. But it seems to the GPG manager. So this might help to export keys in a format that PuTTYgen can load:
Are GPG and SSH keys interchangable?
In general, are you able to connect using any client at all using the keys you have? Then we would have something to begin with.