Blazor has two modes: Blazor client-side is C# code running on a WASM dotnet runtime. It does have the frontend/backend split. Data still has to be serialized (as HTTP calls since that's all a browser can do) but it's done using the same classes & libraries as on the backend.

Blazor server-side has no distinction though because everything is running on the server, and the UI is just a thin stream of HTML updates.

The model you choose is up to you based on resources, latency requirements, payload size, etc. Blazor just gives you more ways to get things done.