Getting on Mac App Store now… This old post helped. 
I already had all of the proper certs downloaded from xcode.
Ran into ITMS-90236 when uploading. Using iConvert Icons app to originally make the icon. I had to do this to reconvert the icon file macos - "Missing required icons" when submitting app with Application Loader - Stack Overflow if you still get the error after this make sure that the 2x files are actually in the icon.iconset folder when you do the second step.
But I think you can do it right the first time with this Mac App Store ICNS Error | Charlie's Blog
It’s probably a good idea to follow the advice here and make the small icons simple instead of auto-generated from large icon but… I don’t expect this to be worth the time as is financially so I’m not doing that. App icons | Apple Developer Documentation But maybe for future projects. Apple seems to not really care about Mac App Store, all of their money is in mobile apps.
Another error I had was “unsealed contents present in the root bundle” when signing the app. I moved everything extra into the Resources folder when signing, then moved it back out after signing and it seemed to work.
Now to finish store listing and submit for review…