There's no reason for the change, but Apple suggests you save it as a movie and upload to YouTube using the dedicated YouTube app instead: https://support.apple.com/en-us/HT211994
Tap Save Video to save the final video in the Photos library on your device. If you have iCloud Photos enabled, you can also access the video from your other Apple devices.
Open the YouTube, Facebook, or Vimeo app on your device, sign in to your account, then upload your video.
There's no reason for the change, but Apple suggests you save it as a movie and upload to YouTube using the dedicated YouTube app instead: https://support.apple.com/en-us/HT211994
Tap Save Video to save the final video in the Photos library on your device. If you have iCloud Photos enabled, you can also access the video from your other Apple devices.
Open the YouTube, Facebook, or Vimeo app on your device, sign in to your account, then upload your video.