Don’t know if this is the correct place to report this, but I feel like keywords and author also belongs in the SEO Meta fields app.
Feature suggestions can be added on the github page for that app. Since it’s more or less only my own little love child developed when I get some spare time at work.
Keywords are intentionally dropped because Google and Bing say they don’t use it, and haven’t for years, so need to bother end user with fields for it, IMO. More info: https://webmasters.googleblog.com/2009/09/google-does-not-use-keywords-meta-tag.html
Author could be added yes, I take that in as a suggestion. Perhaps as a site wide setting and not per content to limit number of fields. Or what do you recon? What’s your use case?