How to get a valid set of data files for FlightGear so it can fully launch

I followed the instructions at StackExchange How to Install FlightGear and also at the FlightGear software developer site to install FlightGear:

sudo add-apt-repository ppa:saiarcot895/flightgear 
sudo apt-get update
sudo apt-get install flightgear

But it does not work. I get this cryptic message that "The requested location '/home/stephen/snap/flightgear/common/fgdata' does not appear to be a valid set of data files for FlightGear'". Indeed the folder /stephen/snap/flightgear/common is empty after the install.

I also tried downloading FlightGear-2020.3.18-x86_64.AppImage and launching it. It gives the same screen. It gives the instructions

"To download a compressed archive of the files click the 'Download' button. Once the download is complete, extract the files to a suitable location and choose the folder using the button above." -FlightGear Software

The only answer to this similar question How to install FlightGear - Flight Simulator received a zero Answer score at StackExchange How to Install FlightGear because (I suspect) that answer does not always work. Indeed, for me, that answer does not work at all to fully launch the software. Only the initial splash-screen can launch successfully with no other viable options to start the simulation.

Please provide specifics of exactly what needs to be downloaded and extracted. (The file name of the required compressed archive would be extremely helpful, along with simple Ubuntu terminal instructions on how to extract it.)

Thank you for any possible comment or assistance in advance.

The problem with those steps listed in the question is that version 20.3.8 of FlightGear is installed without the FlightGear data.

There are a couple of ways to solve this. The way that was easiest for me was to download FlightGear-2020.3.18-x86_64.AppImage found at the 2020.3.18 download image link and also referenced as a link on the FlightGear index page Index of /builds/2020.3. The permission of this AppImage file needs to be changed and then it is executable. Of course, it is still missing the fgdata.

So a separate download needs to be made for the fgdata very specifically for that version 2020.3.18 of FlightGear. It is found at the SourceForge Link to download the 2020.3.18 of FlightGear data. With the Ubuntu files software, it is possible then to create a folder for this compressed data data file, and this compressed data file can be moved into that new folder. And the compressed data file can then be expanded using the right mouse button to select the extract option.

Then when the FlightGear AppImage file is double-clicked from the Ubuntu files, it is possible to navigate to that data folder and load it. The software comes up with a Cessna aircraft and starts up fine.

I am still downloading the 20.3.8 FlightGear data (with the expanded folder name to select as fgdata). It is a very slow process. I imagine that after I download the exact version of the data file for that exact version of the FlightGear application that I should be able to create folders for the data and move it to the right place for the FlightGear 2020.3.8 version to launch without any workarounds.

Update: I downloaded the data-file for version 20.3.8 of FlightGear; then I extracted the compressed file to a uniquely setup folder for it using the Ubuntu files program. After that, I copied the flightgear files to the expected location:

/home/stephen/snap/flightgear/common/fgdata

Note: here, stephen is my user-name in Ubuntu. For your system, substitute your user name. Second, the extracted folder name is fgdata. So this folder is copied (substituting your user name) to:

/home/stephen/snap/flightgear/common/

And everything launched fine; that is just like I suspected it would. From the terminal window, I just type flightgear and all launches fine, thank G-d.

If there are any questions, please comment so I can attempt to clarify anything that is not clear. The process is not difficult, but it requires a lot of patience.

Thank you Ask Ubuntu Community for your inspiration and support.