Welcome friend!
The Notes iOS/MacOS App, in which it uses an IMAP account to store note remotely, is not a service feature. Rather, it is a case in which the software on the phone or computer creates a folder over IMAP on the server, and then stores notes as though they were emails, then reads them back when pulled later. In such a case there would be nothing on our side that would prevent this from functioning, as this simply utilizes default IMAP behavior.
Going back over the settings may help:
On iOS: When adding the account under Passwords & Accounts in Settings, you will find yourself prompted to enable Mail and Notes, youâll need to make sure you toggle Notes on as iOS does not toggle this on by default (opting for iCloud storage as the single default). If you did not enable it on setup, you can go back into Settings > Passwords & Accounts > The name of the account in question > Toggle Notes on. When viewing the Notes app, your email accountâs stored notes should be under your iCloud notes.
On MacOS: Go into System Preferences > Internet Accounts > Add Other Account > Mail Account. Input account information, make sure Notes is checked, hit Done. If you didnât do that when adding the account, go back into System Preferences > Internet Accounts, then click on the email address and put a check by Notes. This will sync in the same way as the iOS account, and therefore share information across both.
