Hello,
Thank you for reaching out to Microsoft Support.
I understand that you're having trouble changing the pen pressure on your Surface App even after reinstalling the drivers. Allow me to ask some questions to further isolate the issue.
To better assist you, may I know which version of Surface App you're using?
Also, have you tried updating your Surface device to the latest version of Windows? This may help resolve the issue.
Additionally, you may try resetting the Surface App to its default settings by going to Settings > Apps > Surface > Advanced options > Reset.
Also run the Surface diagnostic toolkit, See: Fix common Surface problems using the Surface Diagnostic Toolkit (microsoft.com)
If the issue persists, please let me know and we can explore other troubleshooting steps.
Kind regards,
Lavenia