Glad you got it figured out.
And yes, in windowed or borderless windowed mode, the DWM (Desktop Window Manager) forces v-sync. I think the only way you can fully disable it in that scenario is to force it off in the Nvidia control panel or in-game, though it may vary by game.
As stated in my linked post, optimal G-Sync settings are G-Sync + V-Sync on (Nvidia control panel preferred, though in-game is usually fine too) + 100 Hz: 98 fps limit (in-game or RTSS). That goes for both borderless windowed and exclusive fullscreen mode. Aforementioned settings will keep you in the tear & lag free G-Sync range 100% of the time.
I'd also recommend exclusive fullscreen over borderless windowed when possible, as it allows the best performance in the majority of instances.
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