That violates EU law and you can absolutely get a fine for this behaviour. As a digital service offerer you can ask the user for permission to track non-essential information about the user, but your service should work the same, without regard for if that user says yes or no.

If this service is hell bent on raping your privacy, they will have to limit their offerings to mostly those living in dictatorships and immature democracies.

You can just hit the back button and use the website without it popping up again. I refused but they're probably still assigning cookies after I hit the back button.

I'm surprised browsers don't offer something like Docker so that each site is isolated to its own virtual environment.

The creator and maintainer of that extension has passed away in January.

https://github.com/stoically/temporary-containers/issues/618

Chrome profiles work exactly like this, you can set up any number of profiles and they all have their own configuration/sessions etc.

I use home and work profiles on my laptop for instance, works really well.

private/incognito window?

That forgets the whole session when you close it. I meant a way to isolate websites for tracking purposes but also continue to use it over time rather than throwing away all cookies.

It sounds like Chrome accounts might accomplish this for you. I have 7-8 profiles for different personas that seem to sandbox cookies and other identity-adjacent features quite well.

I wonder if their business model is tracking and marketing.

You have to wonder?