Incognito isn't as private as the name suggests. I was surprised one day to open a tab in Incognito and see the site I visited knew who I was. That's because I had logged in to a related site in a tab I'd forgotten about in another Incognito window.

My assumption up to then was that each newly opened Incognito tab or window was it's own private session, but this turned out to be wrong - they all share state, as if you had one separate but shared profile called Incognito. This was a little upsetting as I'd been using Incognito for years without realising the data sharing going on.

Temporary Containers does what I'd expected from Incognito. Each new temporary container has its own isolated cookies etc from all the others. So now I open a TC when I want to visit a site without identity or tracking, or to login temporarily with a different account, and don't use Incognito at all.