Hi ThomasSmallhrf,
Thank you for reaching Microsoft Community. Apologies for inconvenience this has caused you.
May I know which mouse do you have? Is it the Microsoft Surface Mobile Mouse - Microsoft Store?
Kindly try first running these steps on your new Surface Pro 8 to make sure that it has all the updated drivers and software needed then observe if the issue with the mouse persist:
1: Run Surface Diagnostic Toolkit
See: Fix common Surface problems using the Surface Diagnostic Toolkit (microsoft.com)
2: Check for Windows Update
Go to Windows Settings > Update & Security and select Check for updates
Make sure all updates need are installed including Optional updates
3: Update drivers and firmware
Check what is the current OS Build of your Windows version by going to Settings > System > About.
Go to Download driver and firmware for Surface, choose Surface Pro
Then click the link next to Surface Pro 8 then click Download on the next page.
Choose the .msi file that matches your current OS Build and click Next.
After downloading, run and install the .msi then Restart.
4: Run System File Checker Tool
See: Using System File Checker in Windows (microsoft.com)
Kind regards,
Marrion