iphone videos to external drive transfer, iphone storage increasing??

My iphone 14 pro max it nears it capacity (256gb) so I bought a Samsung T7 shield to transfer all my old videos. I started by doing a small amount yesterday and have about 10gb on the drive now. I have deleted the videos I have transferred, however, my storage on my phone seems to be increasing and now I have no space available to do the transfer as I keep getting 'low disk space'. I don't understand why my iphone storage isn't going down although I have deleted the videos and deleted them from the recently deleted folder.

Can someone let me know what I and doing wrong and make it make sense?

Thank you