Anybody ever deal with this one? I haven’t seen much on it so it can’t be common. OBD-II code P0408 indicates a "High Circuit" voltage issue with the Exhaust Gas Recirculation (EGR) Sensor B, meaning the PCM detects voltage above the acceptable range. Common symptoms include a Check Engine light, rough idle, increased fuel consumption, and potential stalling.
Where’s the EGR on this thing? (18 3.5EB)
Figure I’ll pull it and clean it first.

 

Here is what a search of Ford's OBDII Doc shows for years 17, 18 & 19.
In the section on EGR system, apparently the technical writer left out or never updated the info on "B" for the associated 408 code that is 'not' shown.......and does not mention 3.5 L engines, only the 2.7.
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What you have is a Pressure Sensor looking across a calibrated restriction inside the EGR Valve to test flow rate.
The code 408 tells the value expected is out of range >>for some reason. There are transfer charts for A & C but none for B.
Can be electrical, faulty Sensor and / or the EGR is caked with carbon internally or some outside issue with the system.
Anything that affects the Sensing of flow through the EGR System when commanded to function.
Look on the driver side front area for the EGR Valve and supporting component parts.
What it does is gate Exhaust back into the Intake under non-boost conditions to reduce combustion Temps and Emissions under light throttle applications when No boost is being generated.
Good luck.