I added Favored Enemy to a Weapon under modifier but nothing showed up.  Did I enter it incorrectly?

Modifier - Favored Enemy

Subtype - Fiends

Die Type - d4

Thanks

Same here. No idea how to get it to work. Ever figure it out?

That modifier doesn’t actually “do” anything. The only benefit a PC gets from having a favored enemy is this:

You have advantage on Wisdom (Survival) checks to track your favored enemies, as well as on Intelligence checks to recall information about them.

Since there is no way for the character sheet to know when a PC is making a relevant check against a specific type of monster, it wouldn’t know when to display that advantage and when not to. Any kind of “temporary effect” like that is not currently supported.