OpenSSH just deprecated RSA keys. "SSH Mastery" is only 4 years old, but if you follow its instructions you'll get an unusable key. It's a comparatively minor change with a great big impact. Plus there's other, smaller changes.
I don't want to rip folks off either way. So asking you:
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@mwlucas my understanding is the deprecated sha1, which rsa-ssh uses, but there exist other signature algorithms with RSA that still work:
https://levelup.gitconnected.com/demystifying-ssh-rsa-in-openssh-deprecation-notice-22feb1b52acd
I will try some experimentation since the 'key' and 'signature' are different I thought.
