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You picked up some Adware...

The free Malwarebytes may take care of it...

https://www.malwarebytes.com/mac/

Or...

EtreCheck is a simple little diagnostic tool to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac. It will not display any personal info.

https://www.etrecheck.com/

Pastebin is a good place to paste the whole report if you capture the URL while there…

https://pastebin.com/

Workable but harder for me to work with...the Note tool on the bottom of this editor's toolbar, as shown in the image, to copy and paste the output from EtreCheck. In a Reply before you click post, look for this to add longer texts..

See if you have unknown Profiles.

To remove a configuration profile in macOS:

1. From the Apple menu, select System Preferences....
2. From the View menu in System Preferences, select Profiles.Note:
3. Profiles won't be visible until you have at least one profile installed.
4. Select the profile you want to remove, and then press the - (minus) button. Click Remove to remove the profile.

It's probably a malicious extension that's doing this. Check what extensions you have in the 3 dots menu in the top right > More Tools > Extensions. Remove any suspicious ones, or just disable them with the toggle if you aren't sure. If there are corrupted extensions, try the Repair option.

Install and manage extensions – Chrome Web Store Help

Maybe a malware program reinstalled the extension, worth checking if it reappeared. But maybe it's not the extension.

How about 3 dots menu > Settings > On startup? Could be that the ad pages are configured in Open a specific page or set of pages.