As recommended by uni_instructor on this topic: https://lalescu.ro/liviu/fet/forum/index.php?topic=5030.0 , we managed to obtain an AppImage of FET-6.2.2 and GNU/Linux executables which run on decently old systems. You can download these packages from the FET Download page: https://lalescu.ro/liviu/fet/download.html
Please let us know your opinion (if you cannot write here because it is an admin section, open a new topic on another board).