I use a Dell XPS 15 with Ubuntu 22.04 (GNOME). I experienced the same issue, but noticed it works correctly when Unreal runs with the dedicated card. As I use VSCode as my IDE, what I found out to work fine for me is to run VS Code with my NVidia card (right click and press on “Launch using Discrete Graphics Card”), so then any process it spawns inherits the config and runs on the discrete GPU, including running UnrealEngine 5. This is so far the cleanest solution I found to get it to work without needing to care about these details too much 