You are not speaking to Apple here, this is a user forum.
iMovie only uses location information on video and photos for the titles.
They have no interest in you, or where you are.
You may have location services turned on for the camera app, where by all your iPhone photos and video also record where they are taken.
iMovie asks if it can access location services, meaning can it open the videos and photos that contain location data.
It does not track you, or store this data.
Apple is being safe and allowing you to choose if you want apps to be able to access location data, which they would be able to do via the images and video you shot.
This does not mean that it is stored or sent to Apple.
There is no security issue here.
Apple does not care where you are or what you are doing, and they are not logging this information.
If you are worried about someone tracking you then turn off all location data on your iOS device.
iMovie will detect the photos and video that do not have location data and you will be able to "safely" edit these videos and photos without believeing that someone is watching you; which they are not.
If you have location data turned off when shooting video, the iMovie will be able to see these videos even if you choose No to allowing iMovie to use location data.