This guy wants to export a bit rate higher than 66.666mbps!
I don't know whether anyone can cast an expert eye over this problem from the iMovie forum.
The OP for some reason has shot video at 360mbps and is dismayed to find that iMovie can only export a maximum of 66.666mbps.
He is afraid that all the quality provided by his camera will be lost!
Custom export bitrate maximum of 66.667 m… - Apple Community
iMac 27″ 5K, macOS 12.6