Realistic mode is unavailable

If the Realistic button is grayed out, your browser or computer doesn't offer WebGPU, which the Realistic render mode needs to preview thread with lighting and depth. Your design is not affected, and the fixes below either turn WebGPU on or let you work without it.

What you can do:

Use Vector and Stitch modes: they don't need WebGPU and show everything you need to design and check stitches.
On the web, use an up-to-date browser. WebGPU is on by default in current Chrome and Edge (version 113 and later), Firefox (on Windows and Apple-silicon Macs), and Safari (macOS 26 / iOS 26 and later). It is usually not available on Linux (you can enable it behind a browser flag such as chrome://flags/#enable-unsafe-webgpu), on older Intel Macs, or in older mobile browsers. If the button is grayed out, update your browser, or try a recent version of Chrome.
On the desktop app, Realistic mode depends on your system's graphics support.

Example: Chrome on Linux

Open chrome://flags/#enable-unsafe-webgpu in a new tab.
Set it to Enabled and relaunch Chrome.
Reload Boldbobbin. If Realistic is still grayed out, your graphics hardware doesn't support it: keep working in Stitch mode.

Also note: Vector mode is locked while a stitch animation is playing, since there is nothing to animate there. Stitch and Realistic stay switchable, so you can watch the playback in either look.

WebGPU matters in two other places:

Publishing needs a preview image, and only a computer with WebGPU can make one. If you can't publish from this computer, save the design once from a computer (or browser) that supports WebGPU, and it can then be published.
The Realistic preview in the Add shape dialog, the text dialog, and the pixel editor needs it too, and says so where it is unavailable.