not there, so guess follows:

wedges stay in place when you unscrew the bolt.
you must leave the bolt in, but a little proud above the stem surface , then hit the end of the bolt with a hammer. that loosens the wedge.

if you did that, and its still stuck ..

Galvanic corrosion.. maintaing a thin wipe of grease on stem
would have prevented that.. owner error.

tons of stuck stem/seatpost threads, in the past, here, good luck with that..

Ammonia seems a chemical mentioned .

picture 2 is a threadless stem adapter?