Structure Floater Fabric
This interesting mod was created to solve the problem of structure generation in floating island worlds. Normally, buildings spawn at the very bottom of the world, which looks quite strange - imagine houses standing right on the void at level y = 0. This modification allows you to specify in the configuration the height to which all structures will be raised. By default, this value is set to 50.
In the settings, you can also activate an option that prevents structural support columns from sinking into the void. Additionally, an alternative function is available - complete removal of building elements that end up at the bottom of the world, instead of lifting them. You can add structures to the blacklist to exclude them from the mod's processing, but some parts of Minecraft's code do not allow determining which structure elements belong to, so this setting may not completely block the mod's effect on certain buildings.
Currently, the mod affects all dimensions where the sea level is set below the world's minimum y coordinate. This means that the modification also affects the End dimension...

Try this mod if you want to get rid of strangely looking structures in a floating island world!
The mod is compatible with modpacks and can work exclusively on the server side, allowing vanilla clients to connect to a server with the installed modification.