GZGavinZhao As far as I can tell, it has to do with Wayland and NVidia drivers.
I formatted again, and it recognized the second monitor. I have an NVidia GTX 1050 Ti.
After updating everything I was able to use it. But since OBS Studio doesn't work nicely with Wayland(the shortcuts don't work, I think due to Wayland "compartimentalizing" each app, like "sandboxing" them). So I changed to Gnome Xorg from the login menu.
And now Solus doesn't recognize my second monitor again, even when I come back to Wayland