What is the MacBook Pro model?
Does the internal Trackpad works fine?
What type of external mouse (Wired/wireless model)?
For basic troubleshooting try safe mode.
How to use safe mode on your Mac - Apple Support
Note: Safe mode prevents your Mac from loading certain software as it starts up, including login items, system extensions not required by macOS, and fonts not installed by macOS. It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. And it deletes some system caches, including font caches and the kernel cache, which are automatically created again as needed.