"framework can decide what to do with it" sounds like a feature (more flexibility) but is actually often the source of errors and bugs.

A single, consistent, canonical response, generated by the server, taking into account all relevant state (which is stored on the server) is much cleaner. It's deterministic and therefore much more testable, predictable and easier to debug.

For pure UI-only logic (light/dark mode, etc) sure you can handle that entirely client-side, but my comment above applies to anything that reads or writes persistent data.