I call my Grandma most days and have this problem to an extend (although I'm not autistic I think I can respond to this). Me and my grandma have quite different views on most things and we don't have much common interest to talk about. I therefore attempt to talk about things like food, holidays and other simple things that we can all talk about. If you nan didn't want to talk to you she wouldn't facetime you, she's clearly interested. If you don't know what to say, which I too sometimes struggle with, then either ask something completely different or say you need the toilet and will have to let her go (that one always works). I imagine your nan is probably the sort to say things like that without really thinking about the true meaning of said phrases. She's probably also finding it hard to talk about something and wants you to elaborate because she has little to say on that matter.
She often says that she FaceTimes me because she’s bored, so my inference there is that she wants me to entertain her. My mum tells me that my Nan struggles to be entertained without other people, and knowing my grandad, he isn’t the most talkative, so now Nan’s retired and has a lot of free time on her hands, she gets pretty bored and talks to me as something to do. It must be said that I’m not terribly good at idle smalltalk, so after my Nan’s asked me whether I have any news (to which my answer is often no, as I don’t live the most action-packed lifestyle, but if it’s ever yes, I do tell her) and we’ve talked about a few things, I often struggle with other things to say to her and she gets unhappy. I was wanting to improve that for her, as I want to make her happier when she talks to me, even if I’m not the one instigating the conversations. She’s my grandmother, and even though I’m autistic and not naturally the most chatty, I hate the fact that I’m clearly not pulling my weight when talking to her.
I hate video calls, it's awkward, as you can see each other but your not really with them. You are effectively having a phone conversation where you have to look someone in the eye and sit attentively, which is weird. When I'm on the phone I don't sit attentively like I'm in a school lesson I'm probably slouched in my chair or walking around in the kitchen. I gather you are the same or similar in this regard and that's fine and is simply an opinion you hold. If you don't really want to use facetime, tell your nan, in person probably that you hate facetime and that you can't stand it, although you might not want to mention your conversations with her in particular. Alternatively call her before she facetimes you.
I wouldn't worry about it Matt, it's a normal thing, I doubt you and your nan have much common interest and are probably very differently aligned on most things.
I don’t dislike the medium per se (I find video calls easier for things like online learning or meetings where you have a very specific agenda to discuss, but I’ll admit I do often find video calls a bit awkward), and I also don’t dislike my conversations with my Nan by any stretch, but I was more worried that my sub-par smalltalk skills mean I’m not entertaining her adequately when she calls me. I’ll admit I find it less awkward to talk to her in-person or over a different medium, such as over message or on the phone, but she likes FaceTime; whenever it activates as FaceTime Audio by accident (where you’re effectively having a phone conversation and can’t see the person), she will never let our conversation proceed any further until she can see me. I don’t think she’d want to talk to me in person because we live a 30 minute walk away from her house that involves a rather steep hill, which she says she finds hard to walk up. I also can’t get over there in under 30 minutes when I’m on my own, and even if I did visit her more often (we usually see each other in person at least a couple of times a week), I think she’d still FaceTime anyway, as she gets bored at any time of the day and it’s a very easy way to reach me.
I don’t know if I find the in-person conversations with her easier because there’s mostly at least one another person there and it’s not just me and her doing the heavy lifting, which does help me, but I do find it easier in-person, for some reason.
I’m glad I’m not the only one who finds video calls slightly awkward, though… it is nice to hear that I’m not going mad!