Search needs to be a utility.
Browsers need to be a utility.
Email needs to at least have an option that is a utility.
Arguably operating systems need to be a utility.
Adtech needs to either go back to what it was when Google started out (simple contextual ads, no targeting, no data collection, no flashing or popups or video or or or or...), or just die.[0]
The reason these things have all been operated entirely by for-profit entities up to this point is because they're too new for government to have caught up. All the parts of Google that I've named above as needing to be utilities are fundamental, necessary parts of the modern internet, and are basic requirements for the average person to operate in Western society.
> How would spinning off an individual business like Chrome, Android, or AdWords reduce their respective dominance?
As for this question, Google uses the profit from its dominance in adtech to fund its dominance in other businesses. That's the textbook definition of an abusive monopoly. Take away the ad money from the other parts of Google, and they'll no longer have an unfair advantage over potential competitors.
[0] Yes, this would mean that large parts of the internet that have been free-at-the-point-of-service will have to find new business models or dry up and blow away. No, I don't have a silver bullet solution to this. No, I'm not advocating for nuking adtech from orbit overnight with no replacement.