Technology, as you know it is constantly and ever changing for the better.
That being said, YouTube and other websites are also constantly making changes to their websites by introducing newer technologies. Every time they make such changes and introduce newer technologies, it breaks our RealDownloader.
Our engineers have always been able to resolve these issues and as always, we have resolved the current downloader issue.
That being said, can you please do this and let us know if it helped?
1. Open Internet Options from the search window.
2. Under General Tab, click Settings in Browsing History and click View Files. (This will open a folder with a lot of files. Select all and delete them).
3. Close Internet Options by clicking Ok.
4. Using Chrome, Firefox or Edge, go to YouTube.com and play any video and click the Downloader button. (This action will still show "Unable to download" message)
5. Close all Windows
6. Restart your PC
Try and let us know if it helped.