Entra ID - Disabling signup flow adds weird enterprise login options to the sign-in page

In Entra Id, I have an application with a Sign-in user flow. Basically, I want to prevent users to create accounts. Unfortunately, I have not found a way to disable sign-up within Entra other than to use the Graph Api.

But the problem is, when I disable signup using graph api like this :

PATCH https://graph.microsoft.com/beta/identity/authenticationEventsFlows/<redacted id>
Content-Type: application/json
Authorization: Bearer 
{
    "@odata.type": "#microsoft.graph.externalUsersSelfServiceSignUpEventsFlow",
    "onInteractiveAuthFlowStart": {
        "@odata.type": "#microsoft.graph.onInteractiveAuthFlowStartExternalUsersSelfServiceSignUp",
        "isSignUpAllowed": "false"
    }
}

I end up with weirds options being added to the sign-in page like the "CAN'T ACCESS YOUR ACCOUNT?" and "Sign-in options":

The "CAN'T ACCESS YOUR ACCOUNT?" lead to a weird account recovery page that is not the normal password reset page, it has no branding.

The "Sign-in options" leads to a page asking for biometrics... it does not make much sense.

Another problem that arise when trying to sign in with an email that is not in our Entra Id repository, we get this weird error message that is different from the usual "An account with this email does not exists.":
"You can't sign in here with a personal account. Use your work or school account instead."

I've also tried using CSS to remove the sign-up link but it does not work.

How do I disable the sign-up while conserving the same behavior as before doing it?