What does the syntax “(y?)” mean in my woodland mansion coordinates?

Solution 1:

The Y coordinate is undetermined.

Basically, the North/South direction is your X coordinate, and your East/West direction is your Z coordinate. Your Y coordinate is your height.

My guess is that you're searching for a Woodland Mansion since you haven't found one yet, and it's more than likely that those coordinates point to somewhere you haven't been yet. The world generation can determine where on the flat plain (X/Y) to locate objects, but since the world hasn't been generated yet - the hills and valleys, etc, it doesn't know exactly what height it will be at (yet).

You still need a Y coordinate for teleportation, or just ~ to stay on your current height. Alternatively, you can just click the chat output and get the correct teleport command automatically pasted into chat.