I just wanted to make this topic, as the solution to issue I experienced was nowhere to be found.
So after NVIDIA Driver update my Overwatch FPS would float around 60-100 at all times.
Im using a GTX1650S, running lowest settings possible, so this should under no circumstances be the case, and never was.
So I First checked in game settings. All looked good, FPS cap was set to 144, quality settings were seemingly set to “low”. I went forward and reset drivers, did basically everything you would find on forum, including changing power settings, closing background apps and game repair. That repair caused an endless loop of “something went wrong, give it another shot”. So I went forward and reinstalled the game.
This did not solve the issue. After investigating for some time, I found that GeForce Experience was quietly changing my video settings to highest possible, as it was common sense for it given my system performance. Those changes did not appear in game menu, as well as in the looks of the game. Everything in game was seemingly low quality.
Apparently, this caused some conflict, hence low FPS. After changing settings to “max performance” in GeForce Experience, In game FPS stays at 144 at all times.
TL;DR: When your FPS drop suddenly, consider checking video settings in GeForce Experience. Swap then to max performance, see what happens in game. This might save you a lot of time investigating.