A possible reason for your seeing these ads may be because your PC's cookies were retained when you visited some of those sites, or likely those who had online association with those sites. When they recognised you were visiting even briefly, they requested you agree to their cookies, ie. by clicking "I agree", you gave cyber-consent. So when you visit forums such as PC here, any spaces in-between posts and topics will reveal advertising.

I don't use Windows 10 (thankfully yet). I am still using Windows 7. Therefore with regret, I wouldn't know how you would adjust your browser on '10'. But I hope your problem soon goes.