You typically do not download the extension as a standalone file from a website. Instead, it is bundled with the software installation:
If the automatic installation fails, you can often find the extension files locally on your machine at C:\Program Files (x86)\Power Automate Desktop\BrowserExtensions (for newer versions) and manually drag the .crx file into chrome://extensions with Developer Mode enabled. How to Enable the Extension in Chrome
Type chrome://extensions/ into your address bar.
Look for "Softomotive Automation" or "Microsoft Power Automate."
Toggle the switch in the top-right corner to On .
The extension is usually installed automatically when you run the WinAutomation setup. During installation, ensure you check the box to "Install browser extensions".