If I'm not mistaken, nunchuk deprecated the collaborative multisig amongst many people. It was never cross platform though.

To clarify, you can still create a multisig within nunchuk for free with various keys involved, OR you can use their collab multisig where they hold one key. Either setup can also be imported into Sparrow, but the collab option in Sparrow won't be able to ask nunchuk to use their key if needed (you need to use the nunchuk app for that)