Hello, I see a valid subscription for the Adobe account you used to post for help.
With my own subscribed account, I can not reproduce any problem editing video. I'm going to offer a number of suggestions. Please let us know what helps!
In the app settings, under your user name, can you confirm your account status shows as subscribed? Does it help to sign out and back in again? It seems you previously signed in via Apple's login method.
Is it possible that your device is very low on free space? If so, does it help to make more device storage available?
Since you re-installed the app, it could be worth checking camera roll access is OK. In iOS Settings > Lightroom > Photos, can you to try toggling from None back to All Photos?