What browser are you using? I do use Adblock Plus, but when I click on Extensions in Edge it's listed. My Malwarebytes does not show up there because it's a separate program, not an extension. Is this your Windows 11 laptop?
I did find this in a web search:
Okay, first check the Chrome and Edge browser extensions, see if you have any ad blocker extensions, then disable the Chrome/Edge Blocker itself
1. In the upper right corner, click More More and Settings.
2. Click Privacy & Security and Site Settings.
3. Click More Content & Ad Settings.
Select Block ads.
I didn't find any of the things to click on like he said. But in Edge, I did click on Settings and then Privacy, Search and Services. Then I had to scroll down to find the Security heading and there was a switch I could turn off "Block unwanted apps." I don't know if that's the same thing. The original poster who asked the question said the same thing. He didn't find the same path either. His question was titled, "New Windows 11 PC - sites say I am using adblocker- I didn't install one?" Over 50 people said they had the same question. Still looking for an answer though...
Found that someone sent to that Privacy, Search and Services setting and it was set to strict. They changed to balanced and the problem was gone.
And I'm curious - why do you hate your new refrigerator!?