Importing by YouTube link normally works. If one import fails, it is usually specific to that video rather than a problem with the feature.
Try Retry first. Open the Failed tab, find the item, and click Retry. Many failures clear on a retry.
When Retry cannot fix it. Some videos are blocked by YouTube itself — members-only videos, videos with copyright restrictions, and videos limited by region or age. The failed project shows the reason, and for these the answer will be the same on every attempt. Download the video and upload it as a file instead.
You can download a YouTube video you own as follows, then upload the file to Subanana:
Go to YouTube, click your avatar, then go to "YouTube Studio" > "Content" > "Videos" > the options menu of the video you need > "Download" to download the video.
In Subanana, click "Quick Start" > "New Project", then upload the video file.
For other ways to download, see the following article: External link
(Please follow your local laws and regulations, and make sure you comply with YouTube's Terms of Service)