Help with Steam/Valve Proto on Linux

Hey folks,

I have the ultimate FG license and am now exclusively using an older computer running Ubuntu 18.04. I did some research into ways I might be able to run FG on my system and came across the Valve Proto platform. I successfully downloaded the FG demo and input my license key. Initially, I ran the updater without changing anything. Install seemed to run smoothly, but the demo wouldn't initialize after that. I repeated the process, but noticed that the updater defaulted to downloading files to the C directory. That won't work because that's a windows destination. I changed the download directory to be the one that contains my steam files /home/usr/.steam/steam/steamapps/common/Fantasy Grounds. After that, when the updater ran, every update item reported something like the following: HandleFile: Unable to save file(filename/filename.format). The update process concluded with the message "Unable to update at least one product. Please contact Fantasy Ground support."

Does anyone have an idea how to fix this or what might be the problem? I thank you in advance.