In our 2023, the extra ground wire goes to the plastic junction box for traveling lights and brakes under one side of the trailer's A-frame per @Yoshi_TAB 's comment. There's also a green positive wire that doesn't go to the tub, but exits with the other tub wires down where they penetrate the trailer.
If your mechanic was not familiar with the Alde system, you should find out exactly what his process was and report back here. The process is not brain surgery difficult, but there is a procedure to be followed. There are only two types of glycol that have been used in the Alde by nuCamp (edit: in the US). The first was Century. Currently, the Rhomar/Alde fluid is the only thing that is recommended by Alde and nuCamp and will satisfy the warranty.
@Mags80 here is a link to the post I created when I moved the spare to the tongue of my 2018 320S (with lots of detail). I was towing with a 4Runner. You should still be towing level, but moving the tire will add more weight to your tongue. The 4Runner suspension was soft so it squatted, so I had Les Schwab Tire add Sumo Springs to help level. I would guess the Highlander suspension is stiffer.
My 320S was a non-boondock, so wheels/tires were 14".
I assume you don't have a foot plate or wheel attached to the jack post when towing/backing up to give more clearance?
I had to back into the driveway at an angle before straightening out to get the 320 into the garage. It was a standard 20' driveway which meant a lot of back and forth to get the trailer into position once I was over the hump. (I was parking on the right side of the garage but backing in from passenger side blind).