It's the buggiest app I've ever encountered. A few examples I've seen in the last few hours alone:
1. The new "dark mode" periodically sends emails with white background and white text. (Check out their support forum/Reddit and lots of people experience the issue. Users are asked to send it in and… nothing changes.) I've just disabled dark mode because of this.
2. There has been a bug which causes the app to erroneously display "Inbox Zero" despite being badged with new messages. This error has been in the app for 3-4 years.
3. Searching a large inbox throttles up CPUs. On my i9 MacBook Pro CPU usage goes to >250%.
4. It struggles with quotes/signatures. I send long emails which regularly get folded in bizarre places in the preview panel.
5. Periodically hitting forward/reply on an email will not include any of the text in the chain, when the original email is archived.
6. Saw this at the weekend but not today yet: the main window disappears sometimes and can only be brought back by quitting the app and reloading. Right clicking the dock icon and hitting "Show main window" does not work.
Honestly if any other email app was simply designed and had either mappable keys or by default mapped backspace to archive, I'd be using it.