I get this warning when starting up my server in Paper 1.21.11.
[WarpSystem] "WarpSystem v5.1.14_Hotfix-8" has registered a listener for org.spigotmc.event.player.PlayerSpawnLocationEvent on method "public void de.codingair.warpsystem.spigot.base.listeners.TeleportListener.onSpawn(org.spigotmc.event.player.PlayerSpawnLocationEvent)", but the event is Deprecated. "Listening to this event causes the player to be created early. Using the player from this event will result in undefined behavior. Prefer AsyncPlayerSpawnLocationEvent."; please notify the authors [CodingAir].