Either modify the script to construct SessionOptions with SshPrivateKeyPath property, the way I've already shown you on Stack Overflow:
Configure WinSCP PowerShell script to also include a private key

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Or encode the key into the session URL:

WinSCP GUI can generate such URL for you:
https://winscp.net/eng/docs/ui_generateurl#url

Hello
I would like to inquire if it is possible to add a Private Key path to the script referred to here:
Two-way synchronization with delete with SFTP/FTP server

The script that needs to run does not seem to have an area to add a path to the private key.

Is this possible?