Mod version: lostcities-1.12-2.0.4
Biomes stick together (there are never less than three biomes generated near) when using lostcities_bop worldtype (If to use default worldtype or BIOMESOP, they are generated separately).

You're all reporting this but lost cities just uses the biomes as they are generated. So not much I can do about this. In addition I don't understand what is actually wrong

Desert world, and biomes should be single islands in the desert. But when using the parameter level-type = lostcities_bop they are glued together

I still don't really understand what you mean by these islands but I think the problem you describe may have to do with me filtering the biomes because most biomes are restricted. So in other words this is intentional

I don't understand what you mean by 'single islands'?

Like islands in the sea, but in the desert. This concept of modpack - one island, one biome.