to use Geogebra applets offline on the MoodleBox then Geogebra must run completely offline. This means that you can‘t use Geogebra applets saved on an external server. So if you want to use an applet from https://geogebra.org you must download the applets and save it locally on the MoodleBox.
You will find a three point menu and an item "details". Here you can download the ggb file to use it offline.
When you install the geogebra plugin on your MoodleBox you will be asked for two paths. The first is the path to the geogebra library
//www.geogebra.org/apps/deployggb.js ... this is a server in the internet and your applet can't connect it while the MoodleBox is offline. So you need upload this file to the MoodleBox to use it offline. A good place for this file is a folder on the start page of the MoodleBox ... to remember the usage of this file I added a subfolder geogebra and uploaded the file
You get the url of the file with a right click on the file. In my case I got the following url http://moodlebox.home/pluginfile.php/47/mod_folder/content/0/geogebra/deployggb.js
I set the plugin admin setting to this url. I can't say if I need the second url. I don't change it temporarily.
Now I go to my course and add a geogebra instance. You need to add a name and you need to add the content. In my case the content is the file
material-EHBuqva8.ggb. I upload this file and I click the save button. Now I try to use the geogebra applet offline without the ethernet connection of the MoodleBox. Okay, my test geogebra works.
I don't know if we will need the second url in die plugin admin settings ... the url to the
fflate library. I can't say if the download from https://unpkg.com/fflate works for offline geogebra? In my geogebra test I could start the applet with an invalid url
xxx and with the url http://moodlebox.home/pluginfile.php/47/mod_folder/content/0/geogebra/fflate