Haven't been able to get Lost Cities to generate on my 1.16.5 server
Methods Attempted
-editing server.properties generator-settings={"profile":"rarecities"}
-editing server.properties level-type=lostcities_bop
-generating splayer world, pasting lostcities.server.toml into server/defaultconfig
-specifing profile selected in server/world/serverconfig/lostcities-server.toml
-importing splayer world

Ive been going at it for like 4 hours and nothing seems to be working, i know its possible because ive done it before but i dont remember how since its been close to a year since.
Ive mixed and matched the methods above and nothing.

Mods Involved
-Lost Cities
-Biomes O Plenty

-editing server.properties level-type=lostcities_bop

That's not how you do it in 1.16.5. Check the CurseForge page for instructions on how to setup Lost Cities for 1.16 and beyond. It's no longer with level-type