The Lost Cities Mod (1.18.2, 1.6.5) allows players to choose an abandoned city as their world. You can choose ‘Lost Cities” as your worldtype when you create your world. The city you spawn in is an old, partially-destroyed one that overtakes the entire overworld.
The mod is extremely configurable. This mod allows you to create custom buildings or use modified building blocks. This mod can only be used server-side (so vanilla clients are able to connect).