Hi @Joakim
Thank you for reaching Microsoft!
If I understand correctly, you are trying to configure an application which accept known account from Microsoft. May I know what you mean by valid Microsoft account and can you describe "Is there any way to accept all users"
As you mentioned you choose the Supported account types as "Accounts in any organizational directory (Any Microsoft Entra ID tenant - Multitenant) and personal Microsoft accounts (e.g. Skype, Xbox)" by selecting this option you are allowing a wide range of users to access your application with Work or School Accounts any users with a work or school account from any Microsoft Entra (formerly Azure AD) tenant can sign in.
Personal Microsoft Accounts any users with personal Microsoft accounts, such as those used for Skype, Xbox, or Outlook.com, can also sign in