I use outlook for work mails and tried new outlook for a short while. It’s like an alpha version, it’s not even close to feature parity, a pure showcase for a new design. If it ever becomes the only version, I’m switching to thunderbird.
Set up Thunderbird on my work desktop that day, and haven't looked back. Wish I would have way sooner, to be honest.
The interface is far nicer than outlook, but the performance is just too annoying for me.