Problem opening iMovie documents stored in Dropbox folder

The problem in the OP is solved and I think I know the cause.

TL'DR - it was likely caused by me up upgrading to Dropbox's "new MacOS app" which it prompts you to do via a notification in the app. Reinstalled the regular MacOS version solved the problem.

Here are the details -

I called Apple Support about a bunch of things going on with my new Mac (all minor and resolved-ish) and they needed to transfer me to a special group that handles iMovie, got disconnected before they ever gave an opinion on the issue and before calling them back I tried putting an iMovie Library file on Google drive to see if the same problem in the OP occurs. It did not, the iMovie Library file opened normally.

Given that, I contacted Dropbox support rather than call back to Apple.

It look a month, mainly I think due to some staffing issues they were having at the senior tech level, but they advised uninstalling dropbox via terminal commands and then reinstalling. One of the terminal commands errored out, and then they said to just download the Dropbox app again and do a normal install.

That fixed the problem. Now, here is where it get's interesting. Dropbox offered no opinion on the root cause of the problem, but I am a software developer and though I don't do dev on Macs, I can do a cause-effect analysis.

I am not 100% sure what this "new MacOS app" that I reference above in the TL'DR. When talking to a Dropbox senior tech about a different issue last year they told me about it and said it uses something called "file pile" and it's the direction their app is moving in. I can't find the term "filepile" associated with MacOS in a Google search.

In any event, when I was setting up my new MacBook, I clicked on the upgrade Dropbox to "new MacOS app" because I wanted to start fresh with the latest versions of everything.

What I figured out as the troubleshooting was playing out is that upgrading to the Dropbox "new MacOS app" resulted in the Dropbox folder moving from /users/<username>/dropbox to

/Users/<username>/Library/CloudStorage

When I reinstalled the latest release of the "regular" dropbox app, that resulted in a Dropbox folder at /users/<username>/dropbox becoming synced with the Dropbox cloud. At this point, as mentioned, moving an iMovie Library file to this dropbox folder and clicking on it worked fine.

At that point /Users/<username>/Library/CloudStorage/Dropbox existed but it was "orphaned", not connected to the Dropbox cloud and I ultimately deleted this folder on advice from Dropbox support.

My theory is that MacOS considers files in this "CloudStorage" folder to be cloud related and so it pops the error mentioned in the OP.

Rich839 wrote:

It appears from the message you are getting that the file is not downloaded from the Cloud, so you might try downloading it and then opening as the message implies. It could be a Drop Box settings issue with your new computer. For clarity, what do you mean by an "iMovie Library File" and by "iMovie files"? Are you talking about iMovie projects or shared standalone movies from an iMovie project, or something else?

Thanks for the reply!

I did try downloading the file from the cloud and I still get the message. I also tried creating a new iMovie Library file and am able to open it when it is on my desktop if I copy it to the dropbox folder, I can no longer open it (getting the error message mentioned).

To clarify what mean by iMovie Library file -

The data for Projects created in iMovie are stored in /Users/<username/Movies in a file called "iMovie Library". This is the file which I refer to as the iMovie Library file.

Thanks for the reply!

Dropbox is a folder on my local hard drive (Macintosh HD). The folder is not in the cloud. The folder is synced to the cloud.

I agree, something about this folders relationship to the cloud is freaking out MacOS. This did not happen on my old laptop running Big Sur, so clearly Apple changed something and I'm hoping there is a work around.

I will call Apple and post the outcome back to this thread. Thanks again for the reply.

What you described is correct. Except, I have never tested whether a collaborator could open my iMovie Library file back. Under the way things worked with Big Sur, that might have been possible as long if they had a compatible version of iMovie and if iMovie doesn't freak out if it can't access the media source files.

My use case was to keep the iMovie Library file in the dropbox folder, on my local harddrive and launch it from there. I did this because I basically keep all my file in the Dropbox folder. I do this because they are effectively backed up and I can also share any individual file by right clicking and getting a link that I can send somebody.

This works fine with every other application, (i.e. I can open PDFs stored locally in my dropbox folder via Preview, movie files via Quicktime etc.), and used to work with iMovie until I got my new laptop with Ventura.

Last I knew, Dropbox accounts were free, they just had a 5GB limit, so your dropbox folder might be active.

I'll let you know what Apple says.