[halo]

I tried using Multi-Account Containers because I loved the idea but found the user interface rather clunkier and more manual than I hoped.

What I really want is for it to be optimised for the common use case with each domain automatically put in its own container, with some whitelisting of common grouped services (e.g. MS and Xbox Live, Facebook and Instagram).

It's very rare that I actually want to share any cookie info between sites as most of it is tracking. In the rare situation you do, the browser could let you disable containers or add them to a group.

I'd also like something that automatically opts out of tracking preferences, as well as something that periodically deletes cookies/localstorage (say every 14 days).

You could then set it all up and forget about it.

[Copernicron]

I use the Temporary Containers extension and it does much of what you're looking for. I have it set up so every tab is opened in a new container and the container gets deleted when the tab closes. So everything is kept separate from everything else.

[moosingin3space]

This is what first-party isolation is supposed to help with.