finding large videos in the OSX Photos app
Navigate to Pictures folder
Right click on Photos Librar and Show Package Contents
Open the originals folder (prior to macOS 10.15 / Catalina, the 'originals' folder was named 'Masters')
In search bar, type mov, then choose Type 'Movie'
Make sure 'Masters' is still the search target
Right click the column headings and tick 'Size'
Click Size column header to sort


Do not change anything in Finder. Just use it to identify the videos, then go back to Photos to make changes.