OAuth 2.0 compatible with iphone mail?

Hello Buffalo_12,

Thank you for using Apple Support Communities! I understand that you would like to know if the Mail app on your iPhone X will support OAuth 2.0, which is being required to continue accessing your Office 365 email account.

Accessing an Exchange account that uses modern authentication (OAuth 2.0) is currently supported on iOS:

Set up Exchange ActiveSync on your iPhone, iPad, or iPod touch - Apple Support

It's possible there may be additional steps you'll need to take to configure the account on your iPhone once the account has been converted to modern authentication. You may want to consider reaching out to Microsoft, or your IT administrator, to confirm what steps you may need to take when this happens:

Microsoft Support

Cheers!

iOS has supported OAuth2.0 since iOS 12. And it is baked into MS Outlook for iOS for awhile now too (if you use that). Not sure about other Exchange Mail Clients in the App Store though.