Mail has been a cloud service since forever, but since I got my work mailbox that can't just be forwarded to main, I use an app.

Geary seems to be almost exactly what I need UI-wise, but they do not support 2FA.

Funnily enough Microsoft says it will replace Mail with bloated Outlook, so bad decisions are everywhere.

If you read to this point and wanted to say "but on Mac" - that one killed itself for me by disallowing iCloud login in Virtualization Framework-based VMs and by extension any dev tools that require it. It also disrespected me as a user by not bothering to say that outright and wasting a couple hours of my time chasing "Something went wrong" around.

Well there is some variability in that. A lot of the cloud services out there don't work offline at all, suffer from sync issues, have poor quality apps if they even have one or have poor or undocumented privacy architecture.

(I have Apple ADP turned on, so all my keys are on-device only. I also have period of up to 2 weeks where I am completely disconnected from the Internet)

Bloatware? The only thing that matters is the software!

I've run my entire life, business and academic study with this software for over a decade. Works across my computer, ipad and phone. Works offline for days at a time. Never goes wrong.