When using the code

World world = Bukkit.getWorld("world");
world.setKeepSpawnInMemory(false);

in onEnable(), it will still load my world on startup, keeping its spawn-area chunks in memory.

(also using it for world_nether and world_the_end)

This wasn't the case with Spigot 1.13.2, it wouldn't even load the chunks on startup of my server (Preparing spawn area: ...% wouldn't show). But now it does.

441 chunks per world, that of their spawn area