I use Infomaniak Mail or ikmail for short. They give you 20GB free, have a whole suite (calendar and others), and are Swiss based. It can also link to other mail clients under the free tier. Only hurdle is using a VPN or proxy for initial sign up, but that can be turned off for daily usage.

Not sure if this is “that one extension”, but I use Simple Tab Groups for Workspaces-like functionality, similar to Edge and Vivaldi. I know, it isn’t tab groups, but I use it similarly.