Xamarin. Pair to Mac. Key 'OPENSSH' is not supported
I can confirm that user10613465's answer worked in my case.
ssh-keygen -t rsa -N "" -f "%LOCALAPPDATA%\Xamarin\MonoTouch\id_rsa"
In my case I had the correct versions of Windows, Visual Studio and Xamarin. The system passed until tests number 8 and 9 described here: link from official Xamarin on MS Docs
I know it's manner to comment on his asnwer, but I don't have the privillege yet (using work email's StackOverflow account)
I execute below command in command-prompt, and retry connecting Mac.
ssh-keygen -t rsa -b 8192 -N "" -f "%LOCALAPPDATA%\Xamarin\MonoTouch\id_rsa"
-t specifies encryption type 'RSA'
-b use 8192-bit key
-N explicitly specifies empty keyphrase