I've posted before about chrome not displaying correctly in GTA 5, and, as it turns out, standing puddles of water. They seem to not reflect the sky and look kinda black an dusty. I've discovered what is causing it - Reflections MSAA in Graphics Options in the game. Regular MSAA that affects the whole scene seems to work fine, but Reflections MSAA kills the reflections. Not sure why, but I have no problem leaving it switched off. So, issue is solved for me at least. Just thought I'd post this as a heads up should anyone else encounter the same issue.
ASUSTeK COMPUTER INC. PRIME B450M-A (AM4), AMD Ryzen 7 2700X, GSkill 32.0GB Dual-Channel DDR4, AMD Radeon PRO W6800.