If you’re a newbie like me and searching for a way to open the fab plugin in the UE 5.4 in Ubuntu, just download the correct plugin file according to your version of UE from the website, then just extract it somewhere, then, copy the content inside the plugin folder (which you just extracted) and simply paste it in the corresponding folder in your editor’s folder (for eg: mine is UE 5.4.4>engine>plugins). then finally restart your editor again. hope this is useful for some beginners.
credits: @mgni