Hi, @David Moon
Thank you for posting in Microsoft Q&A forum.
If an organisation currently manages O365 updates via SCCM, Microsoft 365 Apps clients receive updates from the Configuration Manager instead of Office CDN.
We can choose Semi-Annual channel or Monthly channel according to our requirements.
How is Microsoft automatically changing the channels here, if we don't opt out?
The change to Monthly Enterprise Channel will mostly happen in the background while your users are using their Office apps. The next time they close all their Office apps, the change to Monthly Enterprise Channel will be completed. If they keep their Office apps open all the time, after three days they’ll receive a message letting them know that they need to close Office to apply updates, which will then finish their change over to Monthly Enterprise Channel.
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