How to block Microsoft forcing Office 365 Semi-Annual systems to the Monthly update channel?

For years, my company has followed the usual software patching strategy of every IT department I've ever worked for, which is to validate new software versions in testing before rolling the upgrade out to everyone else. For Office 365, that means most people were on the Semi-Annual update channel, with only a representative cross-section of test users on the Monthly channel. We're using SCCM to facilitate this, and it's mostly automated except for the rare occasion where updates break something and we have to postpone until we fix the problem.

About a year ago, Microsoft quietly announced that they were going to force some of their customers onto the Monthly Enterprise channel whether they wanted it or not:

Microsoft 365 Apps will be updated to Monthly Enterprise Channel on all your Office devices
Microsoft 365 semi-annual users forced to monthly updates
Microsoft Shifting Some Microsoft 365 Apps Users to Monthly Update Cycles
Microsoft to Move Office Apps to Monthly Updates for Enterprise Customers

All these articles indicate that Microsoft warned users of this change in the Admin Center, but of course nobody saw it before the May 20, 2022 opt-out deadline and we've been forced onto the Monthly Enterprise channel. This is not working for us and we need to go back to Semi-Annual, but it seems like Microsoft is deliberately frustrating any efforts to do so.

There is some invisible setting at the tenant level that doesn't appear in any of various admin pages. I have tried everything outlined in this Microsoft support article, but nothing works.

• Group Policy is set to specifically disable automatic updates and the update channel is set to Semi-Annual. I've verified the policy is being correctly applied on test computers. Office 365 is just straight-up ignoring it.
• The Semi-Annual channel has been specified in the ODT config file and a fresh copy of Office 365 was installed on a test machine using it.
• SCCM is set to manage the O365 client and only the Semi-Annual package and updates are available to agents.
• I haven't set any Intune policies because our devices aren't enrolled in Intune.
• The org-wide 365 channel default is set to Semi-Annual.
• We do not have any servicing profiles defined in the Apps Admin Center. The only option available there is the Monthly Enterprise channel anyway. Even if I were to define one, I'd still have to create and manage an exclusion group that has every computer in it (Azure doesn't have a default "All Computers" group the way AD does).

I even wrote a shell script that removes Office 365 completely, sanitizes the registry, and reinstalls the 2202 Semi-Annual release (the last version before this change was made) with the proper ODT file and Windows updates completely disabled. After about a day, it "fixes" itself with the latest and not-so-greatest Monthly Enterprise channel update.

Microsoft really, Really, REALLY does not want me using the Semi-Annual channel. How do I completely block the Office 365 Monthly Enterprise channel from my PCs??

According to the link: Comparison of the update channels for Microsoft 365 Apps, there are various types of updates, such as feature updates, security updates, and non-security updates.

Regardless of the update channel applied, security and non-security updates are available monthly if needed. Only feature updates, different update channels, the frequency of push is different.

If you want to have complete control over the update frequency, there is a workaround that changing the update source instead of using Microsoft CDN.

For example, you may download the update files to a shared folder in your organization, then update the update files when you need it, and distribute them to clients. But this workaround will increase the control cost.