Components inside the routes/ folder in a fresh app are exclusively rendered on the server. They are not rendered in the client and setting an event handler will have no effect.

Note that this rule only applies to server components inside the routes/ folder, not to fresh islands or any other components.

Invalid:

<button onClick={() => {}} />
<button onclick={() => {}} />
<my-custom-element foo={() => {}} />

Valid:

<button />
<my-custom-element />