Before iMovies was upgraded to version 11 from version 10, users could import projects from the mobile version of iMovie (.imoviemobile) to the OS X version and produce .imovieproject file (and before that perhaps to the .imovieproj file). This doesn't seem to work anymore and there are no news whenever this functionality comes back in future versions.
Convert iMovie project package to iMovie project.
We found one software available in the database for this conversion.
Apple macOS / Mac OS X software - convert imoviemobile to imovieproj on OS X
A proprietary video editor for Mac OS X and iOS
Convert from imoviemobile file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.