Well, here's with an infinite casting shadows, plus one spot in approximately the same position with shadows off. Artifacting is quite a bit better (but not gone - note in particular the spot beside her left brow), though of course the lighting doesn't look as natural.

Perhaps the best I'm gonna do....

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Hardware: AMD Ryzen 9 3900X/MSI MAG570 Tomahawk X570/Zotac Geforce GTX 1650 Super 4GB/32GB OLOy RAM

Software: Windows 10 Professional/Poser Pro 11/Photoshop/Postworkshop 3