When we get a message "ffmpeg not found" that is exactly telling us we have the link two ffmpeg not set correctly.
This might be for a number of reasons however.
The first is that Preferences simply is not pointing to the correct location. For windows this is generally "C:\ffmpeg\bin" assuming you've placed ffmpeg at the root of your harddrive. Adjust as appropriate for other locations BUT... note the 'bin' directory... where the executable files (see below) must be located.
Another would be not all files required from ffmpeg are present. There are typically three files included in 'ffmpeg'... two of which are absolutely required and the third... should sill be there even though not strictly required.
These include: ffmpeg.exe, ffplay.exe and ffprobe.exe
Makes sure you have these three executable files in the directory you are pointing Opentoonz to in Preferences.
If on a system other than Windows the pointer may need to refer to another location and on some systems such as Mac OS you likely will need to allow the executables to run the first time.
The bottom line is that ffmpeg cannot be found so something... a bad download... an incorrect placement... a broken link... a missing file... something is missing.
Cloud drive location? That is a good candidate to troubleshoot... and might be your problem.
Try placing the ffmpeg files in another... harddrive... location.
Rodney