I have read the following question in German Quora:
Ist Deutschland mittlerweile vollständig amerikanisiert?
According to Word Reference, "mittlerweile" means "in the meantime", "meanwhile", but those translations to English don't make sense in this context because there's no previously mentioned time period in which the action being mentioned now occurs. In English, one would only use "meanwhile" if there was one, e.g. "She spent two hours cleaning the house. In the meantime, I bought the ingredients for the dinner"
Duden only provides the same meanings.
DeepL Translate translates "mittlerweile" as "now" in this context. It seems to me another good translation would be "nowadays" (i.e. it's being used as a synonym of " "heutzutage"). Is that right?