RF interference is affected only by distance.  The farther away you can place your USB2 devices from the USB3 ports, the better.

I have a GPS dongle that is USB2.  The RFI affects GPS reception.  I had to put the dongle 6 feet away from the PI on a powered hub.  I played with surrounding the PI4 with foil to test other ways to reduce the noise.  Most of the interference is generated at the connector itself.

The powered hub is required else my GPS dongle doesn't get enough power from USB to be able to generate consistent data.


 

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