Using Classic Outlook on Windows for personal email, calendar, and contact management
@CorBryant,
Here is an MVP article that has another good solution that enables you to switch between Insider builds or leave Insider back to Current Channel, Switching between Microsoft 365 Apps for Business/Enterprise, Current, Preview and Beta Channel (Office Insider) without re-installing - MSOutlook.info.
In Method 2 in the article, he has these reg keys that enable/disable showing the Insider button, https://www.msoutlook.info/files/showinsiderbutton.zip.
After you set the reg key to enable that button, you can then go to File, Office Account, and click the Office Insider button to switch between channels. I had to first switch to CC Preview and then back to Beta Channel. I think the OfficeC2RClient.exe settings were partially applied for Beta and why that extra step. After you use the button to choose CC Preview or Beta, then click File, Office Account, Update Options, Update Now to get it to pull down the Beta build.