I have not bothered to scroll through all the previous 12 pages, but I will share a thought with you about my experience of being married to a neurodivergent husband and raising 2 neurodivergent children - now in their 30s. The behaviour you describe is very typical of neurodiversity and I think, given what you say, I would treat your husband as though he is.
- Changes to routine, whether for good or bad reasons, causes upset and anxiety.
- Knowing you are expected to do something, but you're either not sure what, or are afraid of getting it wrong, causes upset and anxiety.
- Entertaining in your own home or visiting someone else's, without a rigid timetable of what's happening and a list of expectations causes upset and anxiety.
I think you can see where I am coming from here. I suggest that, well before Christmas, you sit down with DH and have a chat about expectations, menus and timetables. If necessary, make notes and give him a summary afterwards. Something like this:
Present for me - I can give you a list for you to choose from (saying where to obtain), or I would really like an x. Shall we go out/look online to choose one? I will buy the presents for others and wrap them, unless you want to help me and we will arrange a date/time. Stick to plans.
Chores before entertaining - list jobs to be done in detail and allocate them to him. Give him a timetable to stick to and try to keep him on track. Front load the tasks so that you are not left with everything to do at the last minute and get stressed.
What to do as a host - again a detailed list of what you want him to do. Take coats, fetch extra seats, take drinks orders (write them down), clear away glasses etc. Don't issue last minute orders and expect him to jump to it. Don't expect him to notice something that needs doing (ask him quietly to do it) and don't pile on further jobs.
Work out some strategies for if he feels anxious/overwhelmed stressed while guests are around. Take any children/uncle/grandpa for a walk around the garden, or schedule an hour or so for anyone who wants to, to have a longer walk. Have a bolthole where he can retreat to clear his head - bedroom, dining room - and if he's going to lose track of time, set an alarm on his phone. Reassure him that he's doing well and that the guests will be leaving at x time (don't issue open ended invitations if it is stressful for anyone who can't judge how long things will go on for. Tell him to take himself off to bed and tell everyone he's had a headache for most of the day. Clear up together the next day.
Being entertained requires similar strategies - fresh air, a bolt hole (car?) and a rough timetable. Discuss menus and what to do if offered something he can't eat.
Above all, offer reassurance and understanding. It will most likely help him cope and let you relax and enjoy yourself. These strategies can work with children too. After all everyone enjoys themselves more when we're all fairly happy and comfortable.
Good luck