1: clean your pc dust etc/might be causing overheat
2: uninstall geforce experience ,no one uses that trash unless u use the recording feature inside(shadowplay or some shit)
3: disable Vsync in game and nvidia control panel
4: go to nvidia CP>3d settings program>add dota2.exe and set quality for high performance and power management mode to prefer max performance.
5: if u have updated/downloaded any software recently then suggest uninstalling them also try disabling antivirus and try to play and monitor the fps.
6:if u have done all the steps above and still experiencing fps issues then do a clean reinstall of your gpu driver using DDU(display driver uninstaller) download and run the software in windows safe mode, after uninstalling run the latest driver for your gpu.
7: run a fullscan antivirus or  malwarebyte.

if fixed for csgo but not d2 then i think the problem is your gpu because csgo is 80% cpu intensive game. Try turning off your pc and reseat your rams and graphic card , just pull out and install back. its worth a try.

then go to steam d2 properties>Local files>verify integrity of game files. If still doesnt work uninstall d2.

your res 3440 x 1440 is really big for dota2 , try enabling blackbar and play with lower res.

is it due to vsync related?

probably GPU issue~ maybe clean GPU and reapply thermal paste?

Its DotA2 update coz the prob.