The lawsuit focuses specifically on search and search advertising. So the answer to your question is Google Search.
Note that a legal monopoly is not the same as the extreme simplification of "zero other options". "In law, a monopoly is a business entity that has significant market power, that is, the power to charge overly high prices, which is associated with unfair price raises." [1]
"In United States v. Google LLC, the federal government alleges that Google has unfairly hindered competition in the search market through anti-competitive deals with Apple as well as mobile carriers. The government alleges that, as a result of these practices, Google has accumulated control of around 88% of the domestic search engine market.
In doing so, the government alleges, Google has additionally monopolized the search advertising market at the expense of competing services. Per the government's estimation, Google has been able to accumulate control of over 70% of the search advertising market. As a result of lack of competition, Google has been able to over-charge advertisers versus what they would pay in a competitive environment." [2]
Statcounter seems to align quite closely with the government's assertion. [3] Extra creepily, it appears to be even a hair worse globally, where Bing is less used (not that I like Bing or MS either). [4] But there is no international framework I'm aware of to handle global-scale monopolies, so that's outside the scope of the suit.
Note that a legal monopoly is not the same as the extreme simplification of "zero other options". "In law, a monopoly is a business entity that has significant market power, that is, the power to charge overly high prices, which is associated with unfair price raises." [1]
"In United States v. Google LLC, the federal government alleges that Google has unfairly hindered competition in the search market through anti-competitive deals with Apple as well as mobile carriers. The government alleges that, as a result of these practices, Google has accumulated control of around 88% of the domestic search engine market.
In doing so, the government alleges, Google has additionally monopolized the search advertising market at the expense of competing services. Per the government's estimation, Google has been able to accumulate control of over 70% of the search advertising market. As a result of lack of competition, Google has been able to over-charge advertisers versus what they would pay in a competitive environment." [2]
Statcounter seems to align quite closely with the government's assertion. [3] Extra creepily, it appears to be even a hair worse globally, where Bing is less used (not that I like Bing or MS either). [4] But there is no international framework I'm aware of to handle global-scale monopolies, so that's outside the scope of the suit.
[1] https://en.wikipedia.org/wiki/Monopoly [2] https://en.wikipedia.org/wiki/United_States_v._Google_LLC_(2... [3] https://gs.statcounter.com/search-engine-market-share/all/un... [4] https://gs.statcounter.com/search-engine-market-share