Hello Raymond,
Thank you for posting in our community. We're here to help.
You may try to resolve the pen pressure issue in the drawing app that you're using by installing the Wintab_X64_1.0.0.20 on your device. Please go to this link, click/tap Download, select Wintab_x64_1.0.0.20.zip and click Next. After downloading, open the zip file and run the WinTab_Setup_64 application.
Note: The download page that you will be redirected to will get you to the Surface Pro 4 Drivers and Firmware download page. Please don't be confused. I would only like you to download and install the mentioned application. Additionally, your Surface Go should also be switched out of Windows 10 S mode before you can install a desktop application. You may go to this link for the steps on how you can switch out of S mode.
If you have additional questions, or if the issue persists after installing the aforementioned application , please let me know by replying to this thread. This way, I'll get notified and respond back to you as soon as I can.