*BEFORE YOU READ* If you have a tablet other than a Wacom product, consider reading this comment/solution! I also updated the link.
Hey I FOUND A SOLUTION!
So you download this english SAI (its legit i tried it and no viruses and no bugs). It wont interfere with the current paint tool sai that you have. You unzip it and put it into where ever (people recommend not putting it in the Program Files, idk). You start the program, and you'll find that while the cursor moves and there is pressure sensitivity, the cursor will be WAY off. So what you do is:
Exit out of sai, and right click the program, go to properties. Then you go to Compatibility, and check "display scaling in high dpi settings". Start sai and see if it works.
If it doesn't:
Exit Sai. Open the misc.ini file via notepad. Make sure TabletCursorMode = 1 and TabletMouseSimulation= 0 Save the file. Re