GPUs don't really have a max screen resolution like that. If you click the spec sheet pdf link, you see it shows different resolution numbers.
DisplayPort 1.2 can support 4096x2160 10 bpc which is wider than 3840. That GPU support DisplayPort 1.4 so it can do even more.
You can connect a 5K 60Hz display using two DisplayPort 1.2 signals (10bpc), or a single DisplayPort 1.4 signal (8bpc).
You can have a resolution of 8Kx8K and have it scaled down to the resolution of the display.
You can do higher resolutions by lowering the refresh rate. You could probably output 8K by reducing the refresh rate to 30Hz in macOS (uses a single DisplayPort 1.4 connection). Windows can connect to an 8K 60Hz Dell display using two DisplayPort 1.4 signals.
Intel GPUs usually have a limit of 4096 width in macOS (except the new 10th generation CPUs) but can do wider in Windows.