It was introduced in 3.1, and I haven’t checked when exactly it was removed but its missing in 3.5 and 3.6. Really unsure why it would be removed because it’s pretty critical if you are working with geometry nodes and want to export your meshes from blender, unless there’s an alternative method.
Just to be clear what is missing, here is 3.1:
Geometry Operators — Blender Python API
The mode option has been removed entirely, including UV Map and all other conversion modes. This is 3.6 but its also missing in 3.5, I haven checked any earlier.
https://docs.blender.org/api/current/bpy.ops.geometry.html#bpy.ops.geometry.attribute_convert
I’m guessing it was prematurely removed in anticipation for UV maps getting moved entirely to mesh attributes? As it is now its a pretty important feature to have for anyone using geometry nodes. Attribute UV’s cant be accessed in the uv editor yet, or exported as far as I know.