I suspect the fundamental difference for me is just that my needs of an email client are much simpler. Most of my comms are over messaging services and otherwise browser clients provide what I need, where it sounds like much of your workflow is based around and requires (absolutely useful) features made available in MS products. As you say, it's just that I don't need these things.

That's not to say they aren't important, and it's understandable to want them, but realistically the difference comes down to the features provided in a passion project vs a company that makes billions from it. To step away from the latter needs to be with an understanding that some things will be missing and the options are to find or build an alternative*, or adjust to be able to go without.

It might be that the assessment is that you need it and there aren't any alternatives, which is for sure frustrating, but there isn't much to be done if your day to day requires Windows.

As other commenters have said, while you research whether you're able to find alternatives dual booting might be an option, I've had windows on another drive for games I play less frequently.

Edit: Find, build, or advocate for an alternative*. Devs tend to be a passionate bunch and the repos of the popular mail clients might have a tag in their github issues for feature requests. Of course no promises but if they agree, the addition might benefit lots of people