@Npin1202 , Thanks for posting in Q&A. From your description, it seems you want the outlook to block add new account. If there's any misunderstanding, feel free to let us know.
I notice you have configured "add new users" as blocked. But it shows not applicable. Please check if your device is corporate-owned work profile.
Based on my research, I find deploy Organization Allowed Accounts mode can allow only a single corporate account be added to Outlook for iOS and Android. Or you can configure conditional access policy to only allow corporate email to access. You can see more details in the following link: https://learn.microsoft.com/en-au/exchange/clients-and-mobile-in-exchange-online/outlook-for-ios-and-android/setup-with-modern-authentication#organization-allowed-accounts-mode
Hope it can help.
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