libykcs11 fails to load key into Windows 11 native ssh-agent

[jplejacq-quoininc-com]

OS: Windows 11 Pro 24H2
openssh: OpenSSH_for_Windows_9.5p1, LibreSSL 3.8.2 (native package that is part of Windows)
libykcs11: Yubico.Piv-Tool 2.5.1
opensc-pkcs11.dll: OpenSC.OpenSC 0.23.0.0

If I follow the instructions provided by Yubico [1] or the substantially better instructions provided by [2], I always get the following error:

> ssh-add -v -v -v -s "C:\Program Files\Yubico\Yubico PIV Tool\bin\libykcs11.dll"
Enter passphrase for PKCS#11:
Could not add card "C:\Program Files\Yubico\Yubico PIV Tool\bin\libykcs11.dll": agent refused operation

The Window event log show two messages:

ssh-pkcs11-helper: error: dlopen C:/Program Files/Yubico/Yubico PIV Tool/bin/libykcs11.dll failed: The specified module could not be found.
ssh-agent: error: process_add_smartcard_key: failed to add key to store. count:-1

I tried numerous variations on forward/backward slashes for directory separators. I always get the same result. The path is correct as well as the permissions.

The Windows native ssh works fine with libykcs11.dll, it's only ssh-add that fails.

ssh-add works fine with OpenSC library, opensc-pkcs11.dll.

[1] https://support.yubico.com/hc/en-us/articles/360021606180-Using-YubiKey-PIV-with-Windows-native-SSH-client
[2] https://gist.github.com/daemonhorn/a6af1b76457b2c10b8058d0a2c919bc3