Take anything from DM with a pinch of salt.  A PS user making money from Gimp. At least that video is not too long, Take out the advertisements and it would be 3 minutes instead of 6 Unfortunately it a demo in Windows not linux
From what I read Chromebooks come with linux embedded and depending on the linux OS makes a difference to the version of Gimp. 
Which sub-version of Gimp? Use the Gimp menu Help -> About and find the version 2.10. ...what 10 / 12 / 14 / 18 /20  Which one ?
Next where to put resources for Gimp. Resources =  brushes  / scripts / plug-ins / fonts / ...etc  Each have their own folder in your Gimp User Profile.
The Gimp User profile is a folder created just for you the first time Gimp runs. Where to find this folder?  
In a regular linux it is 
/home/usr_name/.config/GIMP/2.10/  where .config is a hidden folder - lots of hidden files/folders in linux. Depends on the file manager but look for a view or a control menu or often a shortcut Alt key plus the stop (.) key works
Some Gimps put the User profile in another place. The only sure way to find out is Gimp menu 
Edit -> Preferences -> Folders then look in the entries for brushes .. etc. For example I have two entries  /home/rich/.config/GIMP/2.10/brushes  and /usr/share/gimp/2.0/brushes. The first one is where your extra brushes go.
From what I read the chromebook file manager works overall.  see: 
https://developers.googleblog.com/2019/0...-io19.html
One final check, and this really depends on version of linux and Gimp. Open Gimp and in the filters menu do you have both a Python-Fu & Script-Fu entries of just a single Script-fu ? That determines if you can run python plug-ins or not.
I would appreciate a bit of feed-back it might help other chromebook users.