The button is probably disabled because NIP-07 extensions and NIP-46 remote signers do not support generating adaptor signatures yet (I need to make it more clear someway). It is in my roadmap to add this feature to those NIPs, but for now the only way to generate the adaptor signature is by signing in with an nsec so the client code can do all necessary calculations. This affects only one of the parties of the swap, as I implemented it is the one who sent the proposal in the first place.