Enabling Basic Authentication temporarily only for a few selected mailboxes. not the whole tenant?

Question

People,

Based on https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-and-exchange-online-september-2021-update/ba-p/2772210
The Basic Authentication can be enabled before January 2023.

However, after executing the PowerShell script below, it is still not working.
From: https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/disable-basic-authentication-in-exchange-online#step-2-assign-the-authentication-policy-to-users

$PolicyName = 'Temp. policy basic auth.'  
   
New-AuthenticationPolicy -Name $PolicyName -AllowBasicAuthReportingWebServices -AllowBasicAuthWebServices -AllowBasicAuthActiveSync  
   
$paramSetUser = @{  
    Identity                  = ’Name of the shared mailbox'   
    AuthenticationPolicy      = $PolicyName   
    StsRefreshTokensValidFrom = $([System.DateTime]::UtcNow)  
}  
   
Set-User @paramSetUser   

How to fix the issue above, so only a few selected mailboxes is using Basic Authentication, not the entire Tenant is exposed.

PS C:\WINDOWS\system32\WindowsPowerShell\v1.0> Get-OrganizationConfig | Format-Table DefaultAuthenticationPolicy  
   
DefaultAuthenticationPolicy  
---------------------------  
                             
  
   
PS C:\WINDOWS\system32\WindowsPowerShell\v1.0> Get-AuthenticationPolicy | Select-Object *Allow*  
   
   
AllowBasicAuthActiveSync           : True  
AllowBasicAuthAutodiscover         : False  
AllowBasicAuthImap                 : False  
AllowBasicAuthMapi                 : False  
AllowBasicAuthOfflineAddressBook   : False  
AllowBasicAuthOutlookService       : True  
AllowBasicAuthPop                  : False  
AllowBasicAuthReportingWebServices : True  
AllowBasicAuthRest                 : False  
AllowBasicAuthRpc                  : False  
AllowBasicAuthSmtp                 : False  
AllowBasicAuthWebServices          : True  
AllowBasicAuthPowershell           : False   

Thanks in advance.

Answer 1

Enable it for just the protocol needed if its still allowed to opt-out, then apply an authorization policy to block basic auth for per users, yes. Do not apply to the users that need basic auth.
But not sure if they will still allow an exception, so you will need to follow that doc and see if its possible.

Answer 2

Follow this: https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-and-exchange-online-june-2021-update/bc-p/2599824#M31057
and enable the tenant for Basic Auth powershell

Then Block it for everyone but the required users using an authentication policy

Answer 3

Did you already request an opt-out? It may not be available any longer:
Check from that article
If you still can: follow:
https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/disable-basic-authentication-in-exchange-online#step-1-create-the-authentication-policy

https://admin.microsoft.com/