server version 1.16.1paper
when I use EssentialsX-2.17.2.130,LuckPerms can't find the essentials.fly,but GroupManager can find the essentials.fly
picture ⬇
https://sm.ms/image/l8ywqFjZrYQODUS

If you have two permissions plugins, things break, so just use one.

If essentials.fly does not appear with luckperms, you simply have to type it out and the same thing will happen, as the auto-complete is only a suggestion and does not list everything.