Dell's recent BIOS update for the XPS 15 7590 fixes the GPU throttling issue that was reported earlier. As observed by a Redditor, the new update apparently does not allow the GTX 1650 to cross the 71 °C while also offering some headroom for overclocking with a minimal undervolt.
https://www.notebookcheck.net/Latest-XPS-15-7590-BIOS-update-fixes-GPU-throttling-issues-even-allows-for-GPU-overclocking-with-a-slight-undervolt.428581.0.html