I've used eM Client
for quite a few years now. That's the closest thing you can get to Outlook that's not Outlook. In your IMAP account settings, you can uncheck the "download messages" box. Also, dark theme.
I've also tried Mailbird and liked it, but couldn't use it as at the time there was no no filters functionality. Maybe that's changed since then, but in the meantime I renewed my license to the program above.