I feel for what you are experiencing. I only import YouTube videos. A lot of them (when I can). And it is usually an involved process. If the YouTube video has subtitles provided by the content creator, then it’s pretty easy just by using the LingQ browser extension. However, if the video has YouTube’s auto-generated subtitles, then you will get awful results with that method, so it’s a lot better to do it as a more involved process involving an audio import, where LingQ has Whisper AI transcribe it. Afterwards you add a link back to the YouTube video.
See Youtube import with ai transcript not working? - #12 by ScottTyler
One day I might write up a detailed guide on how I do it, but I just don’t have the time right now.