"Symmetrize armature" flips bones vertically

Question

When I try to copy my dragon's bones to the right side using Symmetrize, they are flipped vertically instead. Before:

After:

I have done my homework. The model is oriented correctly, and the naming convention is followed rigorously. I have tried a lot of solutions (1, 2 (for some reason I cannot set the origin of the armature), 3, 4, 5, 6, 7). No salvation.

Blender version is 2.92.0.

Please let me know what I can do to symmetrise my dragon's skeleton :D

Here's the file: https://drive.google.com/file/d/1B3t23a3seoDxLt-gBZjEaaveng0zwQk3/view?usp=sharing

Answer 1

It turned out that I had an unapplied rotation to the mesh. For reference for anyone with a similar problem: go to object mode, select everything, ctrl+A, apply everything. Then make sure any of your mirror effects still work because now the axis may have changed. Symmetrize works now.