The root problem here is that there's no legitimate way to monetize browser extensions. Extensions are meant to be simple, so it's hard to sell premium features. Extensions usually don't "own" any space to embed ads in.
There used to be. https://developer.chrome.com/docs/webstore/money/ "The web has come a long way in the 11 years since we launched the Chrome Web Store. Back then, we wanted to provide a way for developers to monetize their Web Store items. But in the years since, the ecosystem has grown and developers now have many payment-handling options available to them."
Just want to put a plug in for https://extensionpay.com/ - I've used it in extensions in the past. It takes away the headache of setting up a backend for payment. They do take an extra 5%, but it's worth it especially. for smaller projects