A couple of things: With such low gpu usage I assume you use 1080p in which case there’s no need for the low graphics settings as a 2060S should be comfortable with ultra. LODs (particulary terrain LOD) and traffic settings are the only things you need to keep low although clouds down to high might give a few more fps. The fenix is mainthread heavy so by reducing the imbalance between cpu and gpu performance can only improve.
As for the external drive, the first thing you should check is for firmware updates but also that a) it is not too full (15%-20% free space is ideal) and b) your usb connection (preferably either a blue or red port on your PC) is not allowed to sleep. I highly recommend disabling your packages drive’s virtual cache and increasing the one on your system drive to a (fixed) 15GB.
If your ram supports XMP make sure it is enabled and if it doesn’t then consider an upgrade.