Check the System Settings - mouse, to see if the tracking speed is set correctly. Just changing from 13.3.31 to 13.4 shouldn't affect that.
Are you sure you did the Post Install Root Patches in OCLP after upgrading the system to 13.4?
That, the lack of root patches, would cause a general slowness. You can start up OCLP and try the post Install root patches again, even if you already did it. Just guessing, but after installing the system via the USB installer, did you start up OCLP (copied to the Library/Application Support/Dortania folder) and install OCLP to the internal SSD (HDD) and then do the root patches? That way, you don't need to use the USB all the time.
The nightly version has been updated recently, might want to get the latest version too as the devs are constantly improving it. Edit: OCLP 0.6.6n Updated at 10:15 am, 5-22-2023.