When uploading videos to YouTube it is best to upload from the FilevFolder a not the Photo App. If you upload from the Photo App the app has to prepare the video for upload, which can take a long time depending on the video length. From the File Folder it doesn’t have too.
Logical, because anything in the Files app, has already been exported and prepared as a file that Youtube is likely to understand.
In the Photos app, it's in whatever format the video was taken and likely needs to be converted.
Basically all you are doing is changing when the preparing step is done. When its exported to the Files App, or when it's uploaded to Youtube.
I don't usually upload things straight from the Photos app to YouTube except for shorts so it does not take very long to process those.
Long form videos get uploaded from the Mac from Finder rather than the Photos App.
Uploading videos to YouTube
