I always copy file dates also to the filename like 2023-0711-1018-19.jpg and consider it as the gold standard in my workflow (internal metadata dates are the same but some apps might alter them more easily than the filename. Or vice versa).
I use Final Cut Pro 10.6.8 and maybe iMovie behaves the same.
I always import images and movies from a Finder folder.
But now I tested how FCP imports straight from macOS 13.5.1 Photos system library. Some observations:
I always set new FCP project dimensions manually because otherwise FCP automatically sets the dimensions based on the 1st imported clip. But that does not seem to happen with images because they force the project to the image's resolution such as 4032x3024 and fixing the project back to 1920x1080 needs to first set it as some other resolution and then back. Dragging a movie as the first clip works as usual and the 1920x1080 project stays the same.
Dragged movie (from Photos library in FCP sidebar) preserves its content created date (in FCP Browser). But FCP converts dragged .jpg to .tif (in the Original Media folder) and the content created date is set as current. Both dragged images and movies use they internal Photos name such as A1752040-CF93-4880-8294-A65DC6962185.tiff and 9964E339-AA5F-4CE1-8B97-E0D3908320BF.mp4. FCP by default creates a 10 second clip from imported image.
On the other hand, imported images from a Finder folder stay as .jpg and preserve the content created date and name such as 2023-0711-1018-19.jpg.
So importing from Photos library changes the image dates and somewhat bloats image size in the FCP project folder.
BTW FCP reads the movie date somewhat differently depending how it is wrapped (.mp4, .m4v, .mov) and in which tag(s) the date is (QuickTime, Keys, UserData).
Imported Videos reporting incorrect date … - Apple Community