IMovie won't export in 4K | Simple Fix
If you are editing a 4K Video in IMovie and when you go to render / export the file it only gives you the 1080 output option. Don't panic it really is a very simple fix.
Step 1 Copy all content from timeline. ( make sure first frame is 4K )
Step 2 Close down the project and open a new project
Step 3 Paste all content
Step 4 Go to export file and the 4K option should appear.