Do WyomingMyst’s comprehensive settings guide.
https://us.forums.blizzard.com/en/overwatch/t/guide-maximizing-system-performance-for-overwatch-pc
And if that doesn’t work, and you don’t use your computer for professional video editing/science etc. Then try disabling HPET.
Since that’s rate-limiting your CPU to get really accurate 1/100000th of a second.
But can also interfere with framerate.