About WinSCP public key authentication connection

WinSCP 5.19 released with Support for PPK version 3 keys. (Jun/21/2021)

Starting with PuTTY Release 0.75, released in May 2021, the format of the private key file created by PuTTY has been changed, and WinSCP does not support it as of 5.17.10. Until WinSCP supports it, users of PuTTY Release 0.75 should do the following before saving their private keys.

Key → Parameters for saving key files → PPK file version → 2

Related Information: How to convert SSH key by using PuTTYgen