A newly synced world from Minecraft: Xbox One Edition has the World Type setting set to "Infinite" by default. This world save (before the sync) is set to "Classic" size on the old version and has a nice custom-made boundary.

This may be due to the synced world "Classic" size being too large for "Old" size and must be "Infinite" to fit within the map size restriction. Please add the "Classic" size back to the World Type options so I can import this map.

I do not wish to import and play on this save file until the option to change the world size is unlocked and I am able to set a synced world to "Classic" size before hitting Play for the first time. I am stuck with the old game for now :/