@bradyrands Hi. This is unfortunately a bigger problem that the Pencil2D devs have been looking into. If you want to have a full answer please read my reply on a similar thread: Version 0.6.4 Will not export animation file to anything
Basically Apple won’t allow for backwards compatibility and it drags all of the tech we use with that stance. As the linked reply implies, the only way to currently solve this, while we wait for the devs to provide a bundled solution, is to compile yourself a version of FFMPEG (the plugin that exports) so it works on your system (another user made a compilation guide which is linked in the reply above).
Another idea would be to download an even older version of Pencil2D and use it ONLY to export. Considering we’ve fixed many many bugs over the years I’m not so keen on recommending this, and even now devs are in the process of updating the legacy builds to v0.6.5, the most recent version so users don’t get some of the critical bugs in 0.6.4.
Anyway you should use an extra file copy of your work files to export the movie or GIF (since it could be corrupted and deleted due to previously fixed issues)
This is the repository where all the downloads are stored for the 0.6.X series.
Get either 0.6.3 or 0.6.1.1 and see if those work for export (the FFMPEG plugin should at least be compatible)