I have Autism and ADHD and used to hate visiting and trips out / panto as a kid. Thankfully we usually had a fairly quiet one and my Mum always said that children should be in their own home. As the years went on though, we ended up with all the relatives etc at our house and I could only do the meal then go and hide in my room (whilst the oldies got pissed and loud)
My DD is 13 and is also Autistic and ADHD. The wheels started coming off for her at about 8 or 9, so Christmas has not gotten smaller and smaller over the years. We used to do theatre, a light trail and the Christmas train when she was younger but all of thay has now completely gone. She can't cope with the sensory overload of theatre any more the noise, lights, proximity of people is just a nightmare. We also tried to go to an intimate showing of Home Alone at a small cinema near us 2 years ago and she ran out screaming when a noisy family with small screaming kids sat down beside us. She didn't speak a word for three days (this is when I realised she has situational mutism which has now been diagnosed and she's had help with)
Anyway. After all that waffle, what I'd say is learn what the kids biggest triggers are. When they started happening one after another for me I was just fire fighting and blaming myself for booking all these things cos I felt that's what I was supposed to do as a parent. We are very close and it's just me and her and we are also very similar so it's fairly easy now. I don't make her visit anyone and I don't accept visitors. We plan night where we will watch say, the snowman or home alone with a bucket of Popcorn. We walk around the village of an evening looking at the lights and Christmas trees in peoples windows and trying to spot the Northern Lights. We also might book our familiar cinema at a quiet time and we choose the front row seats because nobody else generally sits there. We bake and we do crafts. She was never one for Gingerbread Houses, but loves to make cup cakes and cheese scones.
One of the biggest things most young people discover about themselves about being Neurodivergent at Christmas is that presents can be overwhelming. I hated opening mine in front of people and appearing to arrange my face in an appropriate manner/ exclaim / be grateful enough but not OTT. It all felt like a lot of acting and it becomes exhausting. My DD likely masked this way in front of me too and now we open at our own pace / when we are ready / no set time. The thing with us is that the ADHD often means we want to rip the paper off everything instantly, but then also get that overwhelmed feeling.
When I book the Christmas shopping slot I ask what she'd like and let her scroll through. She usually chooses some Schloer and sweets and any other treats she likes the look of so thay helps her feel a bit more involved. I also let her pick the pudding we are going to have. She's always loved looking through the Christmas food magazines since she was tiny.
We like fresh air so we go to the woods / beach / Birdwatching as I'm a birdy geek and she actually likes to entertain me with my obsessions. I guess over the years we have found out where our interests overlap and where we complement each other. We both recognise the signs now though if one or both of us is getting overwhelmed.
Don't be afraid to explain to people that you're having to do things a bit differently, and fuck them if you get any comments like "you shouldn't pander to them blah blah" because I spent so many years of my life and my child's life seemingly forcing ourselves to people please at the expense of ourselves. Meltdowns and shutdowns do not make for a fun Christmas, so be unapologetic. I always say that it's a self preservation thing and if people don't understand then tough.
I've just asked DD what she likes most about Christmas and she said being off school and having time to relax, recharge and decompress. The lead up to Christmas at school is a nightmare for ND kids, the usual routines go out of the window and it's crafts, plays, assemblies etc. (Incidentally, DD stopped going to the school panto trip as she couldn't cope with it any more at about 11 yrd old) She says she likes cosy nights with twinkly lights, hot chocolate and blankets and spending time with me. Simple, no pressure, no expectation or low expectation.
DD does love a craft fair as she likes to spend money so we do look for ones that aren't too busy. We like some board games too and things like dominoes, or doing puzzles online together.
Finally, she has a say in the decorations. Her attention span was and is awful so decorating the tree would only last 10 minutes, before she'd wander off, but she likes to put her own little stamp on things here and there with some gothic decorations. (In other words I let her leave some Halloween type stuff out. Lol) We also have an advent calendar of her choosing. Over the years it's been playmobile, pokemon, squishmallows, home made. She loves making one for me too and she gets to open the advent when she wants to. So maybe not mornings if she's tired, but something to look forward to after getting back from school on those weird December days.
Last thing: Food. Plenty of the safe / familiar foods in and no pressure to try anything new. As the years have gone on this had become more challenging for us and DD went Veggie at teatime on Christmas eve last year after she saw my Dad plucking a pheasant. I'd bought the whole Christmas Dinner in including turkey, steak, black pudding for boxing day breakfast etc. She's quite happy with yorkshires, carrots, gravy and mint sauce with some roast potatoes thankfully.
God I'm sorry that was a ramble and a half and I'm not really sure much of it is that helpful. It's just our experience though. As a PP says, definitely ask them for their input too.