You need to add these settings:
options.AddUserProfilePreference("credentials_enable_service", false);
options.AddUserProfilePreference("profile.password_manager_enabled", false);
So your final code will look like this:
var options = new ChromeOptions();
options.AddArguments("chrome.switches", "--disable-extensions --disable-extensions-file-access-check --disable-extensions-http-throttling --disable-infobars --enable-automation --start-maximized");
options.AddUserProfilePreference("credentials_enable_service", false);
options.AddUserProfilePreference("profile.password_manager_enabled", false);
var driver = new ChromeDriver(options);
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