Screw cap stuck in adjustable stem connection, how to remove or reattach?
This is your stem.

As you can see, it is the whole unit from the bars to the top of the fork, including the adjustable bit in the middle. Most dan't have this and I think this is where the confusion is coming from.

To remove your bars for packing, it is usual to remove the 4 bolts on the face plate on the stem. That is the part immediately touching the bars.

After you've removed the bars, you'll want to tape or strap them to the frame somehow so they're not dangling and pulling on the cables. You shouldn't need to remove anything else.

Do not remove the bars by undoing the 1 bolt that adjusts the angle, as you have already, I can't find any diagrams of how it all works.

Do not remove the bars by undoing the 2 bolts that hold the stem onto the fork as this will remove the forks as well.