"Unsupported Graphics Card" in Epic Games Launcher (GTX 1080)

I’m trying to play Fortnite on my PC but it does not work. When I install the Epic Games Launcher (I’m on Windows 10) it throws the error:

There is a problem with your graphics card. Please ensure your card meets the minimum system requirements and that you have the latest drivers installed.

I have an NVIDIA GTX 1080, so it certainly meets the minimum system requirements. The drivers are also up-to-date (I just checked from GeForce Experience) and all other games work perfectly.

How can I troubleshoot this issue?

UPDATE: apparently Steam Big Picture is very laggy, it runs at 1080p maximum and it says I’m running with “Microsoft Basic Render Driver 0 bytes”, as if drivers were not installed. This doesn’t make sense because – for instance – The Witcher 3 runs at High in 4k at decent framerate.

UPDATE #2: now all 3D apps are crashing. I don’t know what TH is going on. Windows Update also just failed, dunno if related

UPDATE #3: I switched my GPU to the Intel Integrated Graphics from BIOS, then I moved my DP cable to the Mobo port and started Windows. At first, Steam still recognised the GPU as “Microsoft Basic Render Driver”, but – after installing Intel Video Drivers – Steam detected my integrated 530 GPU correctly. I started a game with very low graphics settings (I didn’t have my GTX 1080 enabled so graphics were weak) and it didn’t have any issue. After reverting back to NVIDIA graphics, Steam still seems to be using the iGPU. Games will sometimes crash and sometimes work with the NVIDIA GPU, in some cases (e.g. The Witcher 2 Enhanced Edition) a window will pop up saying that Direct3D 9.0 couldn’t be initialized. Witcher 3 works though (unless Steam BPM is also running). I guess I screwed up my install and I’ll have to resort to a C: wipe… Oh, and – quite ironically – Fortnite is one of the few things to work!