Why do you need two DP cables? Is there not enough bandwidth in a single one? I use a 4k@60 display, which is the maximum my cheap Anker USB-C Hub can manage.
Reddit also seems to have some people who have managed to get 144 with FreeSync, but I've only managed 120.
Funnily enough while I was typing this Netflix caused both my monitors to blackscreen (some sort of NVIDIA reset I think) and then come back. It's not totally stable!
It works up until too many pixels change, basically.
https://linustechtips.com/topic/729232-guide-to-display-cabl... is a calculator for bandwidth 4K@144 HDR is ~40 Gigabit/s. You can do better with compression, but I find Nvidia cards have an issue with compression enabled.
I don't think it's an issue until you notice. I only noticed because I toggle HDR for some games and at 1440p240hz, the difference is just enough to not need DSC