The onboard graphics are dependent on the CPU. You could choose a CPU without onboard graphics and still use the Z590 motherboard.I use a AMD 6670 card right now, are the on board graphics as good or better with the z590?
Here is a comparison -- https://technical.city/en/video/UHD-Graphics-630-vs-Radeon-HD-6670 You can probably find others ...10600k