I just bought a 2020 f 150 xlt with tow package I'm now taking it back to the dealership to have a brake controller installed, I looked under the dash and it looks to be a plug and play setup the plug is mounted directly behind the slot where the controller will be installed looks simple. The service department tells me it may require an inline fuse or something to that effect and if so it would be an additional 70.00 charge. I'm scheduled to take it in this week . Does anyone know if this true.

 

If you do a search in the 2015-current forum you will find numerous posts similar to your question. It seems starting MY '18 in the non tow and lower tow package when adding the brake controller no provision for power was left in the power block so an accessory inline fuse was provided as a courtesy. I'm sure this was less costly to Ford than replacing a fuse block. Some even reported finding the inline fuse in their glove box. You would need to verify by looking up the fuse location in your owners manual and see if the spot is in fact populated, meaning the socket is there, you would then need a correct amp fuse.
If you are handy you could save a bunch by doing it yourself. As you found the brake controller is just a plug in module. If you whine enough (or call customer service ) you may be given the fuse. There are several write ups in the archives to follow. You will need Forscan to do enable it. For far less than $70 you can have the controller up and running and have Forscan on your laptop ready for other mods.