Brushes making the program lag and almost crash

I’ve had this one issue happen sometimes but this time it’s making me crazy.
Everytime I try to draw with the brush tool (or any other thing actually, I tried all other tools I usually use, like the fill tool) It lags like crazy and almost crashes the program! I have been able to resolve this in the past by restarting my computer a couple of times but this time nothing works and I am going crazy!
I tried uninstalling the latest Windows Update cause I figured that would be at fault but that didn’t work, and then I tried updating Toon Boom Harmony to 14 and it STILL didn’t fix it!

I use Windows 10 and draw with a mouse.

Which specific model of graphic card is installed on your system?