I used this tutorial to download a plugin: Download UE4 assets from the Epic Games Marketplace using Linux | Alexandra Zaharia
This is still a hassle because the Epic store has no option to add a link to your compiled version from git, you have to install a second version of Unreal Engine, stop the installation process, and then copy your version into the directory Epic Store created.
It worked but now I have another problem: This method may be fine for graphical content, but not for code plugins. The plugin in question is CesiumForUnreal, they say that it is compatible with UE5 and Linux but they don’t provide the binaries in the Marketplace download, so I had to go to their github repository and compile it myself, but it still doesn’t work because the Unreal Engine packaging script refuses to generate my package (RunUAT.sh)
So there are still some major fixes on the part of Epic required to make using UE on Linux a good experience.
Besides that I’ll try to download some graphical assets from the store, put it in my compiled version of UE5 and report back if that works.
edit: Yup it worked, tried this one: temperate Vegetation: Spruce Forest in Props - UE Marketplace
Downloaded it directly into my project with Epic Store under Lutris