[2018 mod to allow AC system to allow windshield defog AND recirculate ?]

If REALLY, REALLY want the vehicle to stay in RECIRC, it is possible to change.  Your local dealer can do this.  It is called a "Customize Function" and more specifically, you want them to change the HVAC "Air Inlet Mode" to Manual, instead of Automatic (The factory default for this mode to to Automatic for the reasons mentioned above by ddswanny).  I would only recommend this for operation in parts of the country with very low humidity levels.

[2016 Highlander Sound System 😩]

KC, the fit and finish of the door panels will be mostly determined by how carefully and neatly you install the noise dampening material.  Want a quiet ride?  It's called a Lexus ☺️

[Discontinued part?]

Just so you know, manufacturers are only required by US law to supply service parts for 7 years after the end of production for that model.

[iPhone features not working with entune system?]

Lyn Finn, It is not the car.  In some cases, Apple chooses not to play well with others (you see, traditionally, Toyota and Apple don't really like each other).  It is not your $48,000 car. (Wait, you paid 48k for a 2018 Highlander?...yikes!)  Anyway, yes, your precious Apple knows this will happen and frankly doesn't care. 🙃

[Vacuum switching valve]

If the drone is most noticeable at a particular engine RPM range (regardless of speed), it is just a normal exhaust drone.

[2016 Highlander, pump like sound coming from the back of vehicle 4 hours after shutdown.]

• kcripper is correct.  It is the on-board vacuum pump running to verify the evaporative emissions system is operating correctly.  You can find this explanation in the owner's manual also.

[HELP WITH 2017 HIGHLANDER CEL]

Fuel, or more precisely, water and fuel mixed in the tank.  Drive it till the tank is empty and refill with quality, fresh fuel.  All fixed.

[2020 Highlander Sightings?]

Well, just spotted one in my garage, if that counts....

4th Gen AWD Limited w/Blizzard Pearl/Harvest Beige (2nd Row Captain's Chairs).  She has a whopping 57 miles on her so far.

 

My dealer installed a Kahu (tracking device) and refused to remove it, so I just pulled the fuse.  All fixed now.  They also pre-installed streaky window tint, roof rack cross bars that I'll never use a, worthless nitrogen in the tires and wheel locks to bump their profit margins. 😣  Other than that, I am happy!