Generally speaking, as you increase the ISO of your camera you lose dynamic range (DR), rather significantly I might add. For example, most full-frame mirrorless cameras can lose up to 3 stops of DR when increasing the ISO from 100-800. But here’s the rub, that’s not exactly right. Huh?
Your sensor has two native points which produce the best results. Long story short (for Sony A7r IV and V): 100 is your best ISO for low noise and DR. But 320 is the next best choice, better than 160 or 250? So generally speaking, if 100 doesn’t do the trick, crank things up to 320.