If you Google Cloudinary Thunkable, the first result should be the documentation for using Cloudinary which includes set up, a video, etc.
Look for the “Upload Media” section of the documentation. Once you generate the green mediaURL block, you can save its value to Firebase. To see what Firebase access using cloud variable names looks like, check out this example:
It took me hours to get this all working. It’s definitely possible but it does take some time to set up and test and troubleshoot.