This might not have helped in this situation, so take following instructions with a grain of salt.

Here’s what I do with quill stems.

1) Hose it all down with penetrating oil. Let sit for a couple days. Might even be worth it to flip bike upside down spray penetrating oil from other side. Charcoal lighter fluid makes a passable penetrating oil if you don’t have any.

2) Turn the bolt on top counterclockwise maybe 3 rotations. The bolt that goes through the wedge.

3) Strike that bolt down pretty hard and fast with a hammer.

4) Strike the quill stem down. Everything should now be freed up. If the quill stem is hard up against the bearing lock nut, maybe don’t strike it.

5) Grip front wheel with your legs and wiggle the handlebars back and forth while pulling them up. Should slide right out.

These steps won’t work if the previous owner messed things up, or if the aluminum stem corroded to the steel fork tube.

These steps work good for generically old rusty parts.

It should be like a 3 minute job.