Fixed: ssh-agent on Windows 10 fails: “unable to start ssh-agent service, error :1058”

PS C:\Users\i88ca> Get-Service ssh-agent

Status   Name               DisplayName
------   ----               -----------
Stopped  ssh-agent          OpenSSH Authentication Agent


PS C:\Users\i88ca>  Get-Service ssh-agent | Select StartType

StartType
---------
 Disabled


PS C:\Users\i88ca>  Get-Service -Name ssh-agent | Set-Service -StartupType Manual

Start manually. This means that as soon as you run ssh-agent, it'll start the service.
Start the service via Start-Service ssh-agent or just ssh-agent.exe.