I have two users on the remote Windows 10 server (Build 10.0.19045.0) - controller (administrator) and worker (non-privileged user). The first user (admin) is able to use Microsoft's ssh-agent correctly. All services can be started or checked via Get/Start-Service commands, ssh-agent.exe and ssh-add work as inteded, etc.
However, when I execute the command C:\Windows\System32\OpenSSH\ssh-agent.exe on worker user, the following message appears:
unable to open service handle
No other details. Exit code 255. No logs. Nothing. Just that non-informative and almost non-googlable message. It worked until a few days ago, stopped working 2 days ago.
Update: Workarund
I've found a dangerous and unwanted workaround by granting worker user administrator privileges, but as I understand, this should not be the requirement.