The start page is one of the most obvious places where they can do that. When you open a new tab, most browsers have a default start page, and what is on that page may depend on where the money is to be made. Google Chrome, of course, will give you a search box for Google. Microsoft Edge will try to plaster your start page with news feeds and other things Microsoft is sure you are interested in; you can pare down those extraneous details in the settings, but you can never get rid of the centrally located search box for Bing, the Edsel of search engines.
Dr. Boli, who is older than many people, remembers primitive days when it was possible to set the new-tab page to utter restful blankness, but that does not seem to be possible anymore. Fortunately Firefox will allow you to replace your new-tab page with any arbitrary page on the Web, and for Chromium-based browsers like Chrome and Edge there are extensions that will accomplish the same thing. But what page will it be? Most of the pages on the Web are also filled with distracting things you want to avoid.
As a public service, therefore, Dr. Boli has provided a start page for your new tabs, a page that does absolutely nothing. It is possible that the picture will change once every few weeks (it is also possible that it will not), but there will be nothing to interact with, nothing to distract you from the business at hand. You can find it here:
Set your new-tab redirect to that address, and get back to getting work done when you open a new tab.