Importantly this just works which is more than I can say for anything else I've tried ... anecdotes below...
I was using Fastmail before which is a good cross platform solution but the whole solution goes down the toilet if you want to use their official apps and offline support. Third party mail clients are almost universally complete garbage due to disparity over IMAP mailbox naming, sync issues and corruption. I haven't found one that works properly.
I fell out with Google and GSuite before this because something fucked up my domain provisioning and they couldn't fix it via support. Also I found out rather rapidly that the moment I converted my account to a paid GSuite account that my YouTube account required a $30 payment to be made before I could post videos to my own channel suddenly. They held my YT account to ransom and couldn't fix a provisioning issue. No chance. I will never deal with them again.
On Office 365 I deal with this at work every day and it's horrible. It started off reasonable but the feature load is weighing the whole solution down and now it's a crapfest of pain. Even the authentication processes are utterly painful every day requiring a half arsed authenticator app that works 50% of the time. I still maintain an office 365 family account so the kids can use the desktop apps for school work.
As for privacy, I think it is well oversold in the email space. The communication protocols don't guarantee privacy and no legal jurisdiction is particularly friendly. I think it's better to focus on deliverability and using another technology for secure or private communications. I myself use email only as the usual e-commerce and event receipt handling system. Out of the 100 or so people I have in my contacts, only my mother still actually communicates via email.