I've only had to deal with this once. Candidate was mid transition, but had fully transitioned socially. Presented as female, known by their chosen name etc. Passport and all right to work had their deadname.Everything official went by their deadname, e.g contract, payslip, all the HR bits. But publicly they were female, email address was their chosen name, name badge, pronouns etc were what they were used socially.

The best way to deal with this is by having an honest chat with them. Most people transitioning understand that until legal documents change then certain things will still have the deadname on it.

In reply to Ryan:

You can always state you are happy to reissue the contract in their new name once all legally finalised, that may make them feel more included/understood

In reply to Ian:

thanks both!