The PacketEvents.getSettings().useProtocolLibIfAvailable(boolean) setting is most likely not be coming back.
Recommended to have ViaVersion, ProtocolSupport or ProtocolLib on your spigot server, as PacketEvents makes use of them to resolve client version ONLY if they are available.
NEW FEATURES
Official 1.16.4 support ClientVersion.v_1_16_4, ServerVersion.v_1_16_4 created
BUG FIXES
Bungee client version resolving bug fixed One of the recommended dependencies(ViaVersion, ProtocolSupport, ProtocolLib) are only required on the spigot server if you have a bungee network.
Interruption of PacketEvents.stop() protected(Two plugins calling the method will no longer break PacketEvents)