Hello, i've made ULMB working with G-sync at the same time while running 155hz on my PG258Q.
For what I've tested i can't strobe using default refresh rate, This means i coudln't use 60 100 120 144 240hz,
because If the monitor finds a default refresh rate, It will activate G-sync and i wouldn't be able to enable ULMB.
So, this is how i proceeded:
1. On Nvidia pannel you need to change on Manage 3D settings, Preffered refresh rate set to Application-controlled.
// I suggest every time you start your game you check this voice, because something Nvidia change this parameter
2. You need to create a new resolution. At the momemnt I use 155hz and is a really sweet spot for me,
However you just need to change the Hz in something no default, But I can give you other different settings for other hz
These are my settings for 155hz
https://i.imgur.com/CuEBEKv.png
3.Now enter in game and select your new resolution and exit
4.Active G-Sync and join the game
5.Now you are enable to active ULMB
PS.
I try to add 5 to vertical total pixel too, everything is the same so you just no need to do that.
Remember to cap your FPS -3 of your hz, cap 152 if you play 155hz
There is just a little issue with this, in game you can have some little change of brightness sometime, because you have like 155 refresh rate capped to 153.
Wanna avoid this? You can, is just a your preference there is just a compromise.
If you cap to the Max, like 155hz, you have some tearing on the screen, not so annoying but still better than no G-Sync.