Will serps change when DA updates now in 21 July? Or does google have a Da update that it does on auto before the index updates?
Domain Authority has nothing to do with Google and won't affect when serps change. Google results change hourly these days... always.
There is a correlation, but not a causation. Domain Authority is a prediction of how a site will rank... developed by a company that isn't Google (Moz). https://moz.com/learn/seo/domain-authority
yes agree with you DA toolbar is created by Moz Which tells your website page Authority and Domain Authority. i suggest you to get backlinks from high domain authority websites if you want better result in google.