A lot of folks here wants you to ask him what he wants.
Be prepared to hear that he doesn’t know what would help. But he will appreciate that you’re giving him agency.
One of the challenges I have with this question as someone who is mainstreamed, profoundly deaf (this means I don’t know sign language) is that deafness takes a number of forms, so there’s no real one size fits all solution.
But far be it for me to point out problems not suggest solutions!
* ask him if it would help to provide a real-time transcription service. This is not an automated system but a specially trained human who will transcribe meetings in real time.
* ask him if he wants someone to write a meeting summary that captures decisions made, action items delegated etc. then make sure that happens.
* ask him if an ASL interpreter would help.
* sign up for sign language courses yourself and use your professional development budget to pay for it. If he doesn’t know ASL ask if he would want to learn also. Pay for his training.
* help him find a professional community of deaf persons to be a part of. Give him options. No group is perfect for everyone.
* the biggest barrier he will face in his life is isolation. So support him so that he doesn’t feel isolated.
* if your company throws company events for everyone to participate in, try to create a something similar, running concurrently, that’s accessible for him. Solicit ideas from him but it could look like a small group chat online or playing games online.
* hearing aids (if he needs them) are REALLY FRICKING EXPENSIVE - benefits typically cover up to $500 and aids can cost $2-7K. Offer to buy his next pair.
This is all off the top of my head. I could probably think of more with some time.
I hope this helps. Thank you for taking the initiative to make him feel part of your team.
(Edit: formatting)