Describe the bug
"Uncaught DOMException: Failed to execute 'querySelector' on 'Document': '#'" is thrown when loading a build. No errors are thrown when using default Unity WebGL template with index.html.

To Reproduce
Steps to reproduce the behavior:

1. Build empty WebGL build in a react-unity app.
2. Notice WebGL build not loading with "Uncaught DOMException: Failed to execute 'querySelector' on 'Document': '#'" error.
3. Add ID to canvas, reload.
4. Build works with ID on canvas.

Expected behavior
Same content built with Unity 2021.1f14 works seamlessly with same setup.

Screenshots
N/A

Details (please complete the following information):

• React Unity WebGL Version: 8.4.9
• Device and OS: Win10
• Browser: Chrome 92.0.4515.107
• NodeJS Version: 12
• Bundler: Webpack 5.5.0

Additional context
N/A