Well, Vpatch Does a variety of things
1. Lowers Input Lag (Which is essential for games like these)
2. Enables Higher Resolutions (Even though it will be more pixelated, It must be configured via the Vpatch Config file)
3. For TH12 it fixes some score bugs from what i can recall
Also For Older Titles Such as Touhou 6 & 7 it Fixes the High Framerate Issues (Which makes the Gameplay incredibly fast)
You may download Vpatch here: https://en.touhouwiki.net/index.php?title=Game_Tools_and_Modifications&Vsync_Patches#Vsync_Patches

If The game crashes when trying to run Touhou Seirensen with the Vpatch then you have found the right place (This happened to me, And that is why i created this guide)

It happens because Valve’s SteamStub DRM prevents the Vpatch from working

Make sure you have Vpatch in the install directory of the game
Step 1. Download This: https://drive.google.com/file/d/1q2RXbLWICxCJzSa5iWzIQSWBmudnghTl/view
Step 2. Extract it. but dont run it yet
Step 3. Open Steam
Step 4. Find Touhou Seirensen ~ Undefined Fantastic Object in the game list, Right Click it, Manage and then click Browse Local Files
Step 5. Drag the Files from th12vpatchfix into the th12 Steam Install, and replace the files if you get a prompt
Now you are done. You may run Vpatch now
If you are using a tool such as THCRAP, Remove the game from there and readd it with the Vpatch inside of the game install, if you didn't have it when you added it to THCRAP

If your Anti-Virus is constantly removing the installation, Try excluding the Steamapps folder from your Anti Virus Software (Such as Windows Defender)