Unfortunately, google oauth2 "web application" client doesn't really support code flow with PKCE even for now https://stackoverflow.com/a/63275535/20240963.

But the "UWP" client support PKCE https://developers.google.com/identity/protocols/oauth2/native-app#step1-code-verifier. So there is a workaround that you create a "UWP" client, then the authentication will success.

Credentials -> Create credentials -> OAuth client ID -> UWP You could use this "UWP" client for Blazor WASM. And the store ID can be whatever.