This problem is specific to MSI installation only.

Problem statement
If you install the V8.9 through MSI then ssh-agent doesn't have all the required privileges. This effects the FIDO / PKCS11 scenarios because the ssh-agent fails to create ssh-sk-helper.exe / ssh-pkcs11-helper.exe.

Work around
Please use zip payload for installation instead of MSI package.

Code snippets
Install-sshd.ps1 has the required privileges. Code here.

MSI is missing the required privileges. Code here