K-9 seems promising, it is acquired by thunderbird and planning to become thunderbird bird mobile. It has office 365 support, but IIRC it is pretty convoluted to add a office 365 account. https://www.f-droid.org/en/packages/com.fsck.k9/
I used to use K9 long time ago, but had issues with notifications not working properly. I've been using something not FOSS which was OK but I wasn't 100% happy with. After reading about FairEmail on another thread the other day, I've now adopted that and so far it is working great. It has way too many options though!