iMovie Library is HUGE... too much memory being used (SOLUTION)

I noticed that my 2TB hard drive was almost entirely used up and saw that my iMovie Library was ~750GB which didn't make any sense given that I only had a few videos in iMovie and I had deleted the media. I tried all the solutions I found on the web but nothing helped.

It turned out that the iMovie library was so large because I had provided iMovie access to my photos.

To undo this, go to settings / privacy & security / Photos... and then turn off iMovie's access to photos. This instantly shrunk my iMovie library to almost nothing, freeing up one-third of my hard drive.

Problem solved.