Entitlements are flags (like AndroidManifest permissions) for apps allowing them to do things. It’s not something a user will ever encounter.
In this case it is a flag indicating to the reviewer etc that the app links to a website for account creation and management rather than doing it all within the app.
To me it seems the very distinction is toxic. All users of a platform should be considered equal, not separated into developers and consumers. Creating your own apps for whatever an audience to use it (for yourself, for specific people you want or for everyone) should be considered a normal feature any user may use.
WTF this even is? I have no idea what could "The External Link Account Entitlement" mean.