curve25519-sha256 kex not supported in WinSCP

WinSCP Version 5.17.5 on Windows 7 x64. It has not worked on any previous version of WinSCP either.

Using SFTP. Using GUI.

The remote server is configured with:
KexAlgorithms curve25519-sha256

Please note that curve25519-sha256 is the newer name for the deprecated curve25519-sha256@libssh.org

I get the following error when trying to connect:

---------------------------
Error
---------------------------
Couldn't agree a key exchange algorithm (available: curve25519-sha256)
---------------------------
OK Reconnect Help
---------------------------

Log attached.

This request has been added to the tracker:
https://winscp.net/tracker/1865

Can you send me an email, so I can send you back a development version of WinSCP for testing? Please include a link back to this topic in your email. Also note in this topic that you have sent the email. Thanks.