My work HIPAA compliant encrypted email through Microsoft exchange works with apple's mail and calendar apps, so I don't necessarily understand why that couldn't be the same for Proton, especially if it just works through a device management profile like how desktop proton bridge works for the apple mail app.

I am not asking this because I think there's something inherently wrong with the Proton mobile apps, I am asking because I would like one app where I can view all of my inboxes together (same for calendar). I personally have my personal proton mail inboxes as well as Microsoft exchange inboxes for work and for school, and a lesser used iCloud email address, and a google account created with my proton mail email so that family who uses Google Calendar can share their google calendars with me without having to make their calendars public. I prefer the apple mail and calendar apps because they allow me to view all of these calendars and inboxes together, regrettably except my proton mail account.