Where did you find that {QueryString:}? It's not mentioned in the docs: https://learn.microsoft.com/en-us/azure/active-directory-b2c/claim-resolver-overview#oauth2-key-value-parameters.

You need to use {OAUTH-KV:any custom query string} instead.

E.g. {QueryString:EntityId} should be {OAUTH-KV:EntityId}.

Or if this is in fact a SAML policy, then you need SAML-KV instead: https://learn.microsoft.com/en-us/azure/active-directory-b2c/claim-resolver-overview#saml-key-value-parameters.