Everything else. Cloud provider, operating systems, browsers, hosting business apps, phone licenser, Internet provider, smart home manufacturer, and various moonshots. Their ad company is a monopoly because of those other services.
Google as an ad company that can't leverage those other lines of business to gain an advantage over other ad companies still has a viable ad business. They can compete on the basis of that lone company's strengths.
("If you're nothing without this suit, then you shouldn't have it")
I see your point, but also, if Google continued to own all these other things, it would still be a terrifyingly large spread, no?
Who gets what part of the company is the wrong question to ask. The org chart would get split along those business units. In all likelihood, the company called "Google" would be the software side, since that's where search lives.