Yes, it does work on lethals!
Lethals can be stored in your pride dynasty. in fact many people had lethals stored in their dynasty for years before the Canopic Jellyfish was introduced and were able to use it on those lethals.
I recently had a lethal born myself. I let it die and then brought it "back" with a Canopic Jellyfish.

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Wait until they die and then go to the items page and pick the chosen lion from the drop-down menu.
If you look at you Canopic Jellyfish right now you should be able to already see your dead lions that you have stored in your dynasty as possible options to use the item on.

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Does it work on lethals in that case? not sure if they can go in pride dynasty (never had a lethal before!)

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Aah, main chat said that a canopic would work, oh dear. Thank you for letting me know!

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AAA, Valana, thank you so much, I'm so confused, eee

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You're welcome!

Just in case you are still unsure, this is the leathal I used the Canopic Jellyfish on.
As you can see from the link the cubs ID is 794135404573.

And here is a screenshot from my userlog showing that i used a Canopic Jellyfish on that cub with the same ID.

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@Valana, no doubts but I really appreciate you going to the effort, thank you so much <3

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Apologies, I heard different information! Thanks for the clarification ^^

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