There is nothing I know of in the Z590 chipset that would prevent the iGPU from being supported.  Of course, the first step is always to get /dev/dri to show up if you want to use the iGPU for hardware transcoding.   In the case of the last few motherboards I have used with hardware transcoding, setting the primary graphics adapter to onboard, iGFX, IGD, etc. according to the BIOS is all that was needed to cause /dev/dri to show up.  Do not set primary graphics adapter to Auto if that
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