If you can't download drive files for iphone for offline usage, you can try this method.
Copy the link of file you want.
Go to https://bytesbin.com/google-drive-downloader (by clicking this link).
Paste your link in relevant place.
Click on "Download" button.
Again click on "Click here to download" button.
Most of Videos are formatted as ".mkv" videos.
Therefore, they may not play with your inbuilt video players.
Try them with Video players such as VLC media player. (through all platforms)
To download VLC media player
Click here (Android)
Click here (Apple)
You should log with your university Email Address.
Click here and log with your university Email address.
Make sure, You are using latest version of Google Drive app then Update into latest version of Google Drive app through Play Store or App Store.