External Identity User Flows: Disabling Sign-up in a "Sign-up and Sign-in" User Flow does not Take Effect when demoing via the "Run User Flow" interface

Overview:

Our team recently created a "Microsoft Entra ID for Customers" resource which we are attempting to configure for our use case. For said use case, only customers with pre-created accounts should be able to access our application. As such, we need to disable the "No account? Create one" button that is inherent to the "Sign-up and Sign-in" User Flow. Notably, no UI control exists to do this within the Microsoft Entra admin center.

Steps Taken:

After looking through the existing Entra ID documentation, we stumbled upon the following article which seemed to perfectly encapsulate the problem we needed to solve and prescribed a solution to it:

https://video2.skills-academy.com/en-us/entra/external-id/customers/how-to-user-flow-sign-up-sign-in-customers#disable-sign-up-in-a-sign-up-and-sign-in-user-flow

We followed the specified steps to obtain the ID of our User Flow and gave our Application the necessary API permissions to accept the request. After a time, we were able to successfully make the PATCH request specified in the above documentation. After receiving a 204 (success) response, we navigated back to the Microsoft Entra admin center > External Identities > User flows > Our User Flow and clicked the "Run user flow" button. Much to our dismay, the "No account? Create one" button was still displayed.

To triple-check that we didn't make a mistake, we followed the documentation below to view the JSON representation of our created User Flow via a GET request. In the response JSON, we confirmed that the isSignUpAllowed property was correctly set to false:

"onInteractiveAuthFlowStart": {
                "@odata.type": "#microsoft.graph.onInteractiveAuthFlowStartExternalUsersSelfServiceSignUp",
                "isSignUpAllowed": false
            },

https://video2.skills-academy.com/en-us/graph/api/identitycontainer-list-authenticationeventsflows?view=graph-rest-beta&tabs=http#example-4-list-user-flow-associated-with-specific-application-id

Problem & Assistance Needed:

Having performed the steps above, our understanding is that the "No account? Create one" button should be disabled since the "isSignUpAllowed" property is set to false for our User Flow. Given that it's still appearing in the User Flow "run flow" preview, is this a bug/known issue? Is this a problem specific to just the User Flow preview? Is there a different "type" of User Flow we can create that doesn't enable sign-up (it doesn't look like it)? Is there something we're missing or something else we can do?

Thanks so much for any help, guidance, or direction!