Thanks, you’ve found a bug in the Web Spinner.
Both desktop and Web Spinners default to Active = False. On desktop, that correctly leaves the busy indicator blank. The Web version currently still draws the arc and only stops its rotation, which explains the difference.
Setting Spinner1.Active = True, either in code or through the inspector, should show and animate it when the application runs.
I’ve logged the bug. I will fix the Web version so an inactive Spinner is blank, and add regression coverage for its initial state and switching Active on and off.
In Studio’s designer, both versions should remain visible as static previews regardless of Active, so you can position them without distracting animation. That behaviour will stay.