Found it really interesting to read the response that detailed a specific methodology of passing on news - allowing for time to process before a conversation was had. I think it's worth trying!
My own mum passed away a long while ago when I was quite young. I had the trouble being discussed in the OP with my Dad. I think I was kind of hoping he might step somewhere in the direction of the void my mum left but he never did. I'm absolutely sure he was autistic or at the very least ADHD. It helped me to see him in this light so I didn't take it personally. He was so easily distracted during conversation and would always turn it to something that interested him. In his later years I would always have to call him not wait for a call (which I'd never get) and I'd have to ask him about which car he was doing up or I wouldn't really get a conversation. At one point he was seriously ill and refused to speak to me for a number of months so I can't say things were one sided because he wanted the attention on him. It's like he just didn't really want the connection.
When he was dying, I went to see him. He tried to put me off but I went (he lived in a different country) anyway. He seemed to warm a little and even said he thought I was the only one on the same wavelength as him (because I was the only one listening to him and trying to improve his situation, I can't tell you how sad that made me). I mentioned his previous illness and the communication shut down and he said he was aware of it. Then he said he thought I should buy some shares (whilst I was sat in the hospital at his bedside) because then we'd have something to talk about. He didn't see how the two types of scenario weren't related. He literally didn't know how to relate to anyone if it wasn't about something physical/ practical. I hoped he might say something before he passed away about opportunities for connection being lost. But as he'd never seen them, they weren't missed out on, they simply didn't exist. In the end, save for his life story, our conversations were very banal and mostly about the logistics of medication and that was that.
I do miss him. I'm now realising that, along with calls to tell him what we'd been up to, I used call him when I was feeling very low and didn't feel like I could call anyone else. Sometimes I'd try to outline the current problem (to def ears). Other times I'd just not say anything and just ask what he'd been up to and talk cars. Yes it was frustrating, and in those situations I didn't ever come away feeling like I felt better for it. But maybe I did?! Sometimes it was just a distraction. Sometimes I was angry that he'd missed the point and started talking about cars again. But I guess my life had moved on a bit in that half hour conversation and I was able to then move to the next thing. Maybe like it grounded me a bit? The thing I miss most is having an excuse to call him - just because he was my dad. I don't really feel like I can just randomly call others in my life without a purpose. So yeah, that's been a bit shit.
I guess, for that reason I don't necessarily see the benefit in going NC as it might not make you much happier. For what it's worth, the example you gave about the bus and the colour, that would likely be my dad! Although, maybe the model instead of colour! It's almost like, they've not been knocked down by a bus before so don't know how to talk about it, but they have seen lots of buses and so get side tracked by the bus itself.
I'm aware I've waffled but I've been thinking about this a lot the last few days and wondering would I have done anything differently if I could. I don't know.
What I wanted to add finally though was about the stories other people are telling where they were conversing with their mum about something and she replied with the same story (or something that is perceived by the OP as worse - ie one upmanship) happened to her. That sort of stuff gets mentioned all the time in terms of ADHD - people use it as a way of trying to show empathy and find common ground. I catch myself doing it often but try link it to further questions. I'm not trying to "out do" anyone at all. I wonder if those people took this kind of thing as an invitation to engage in further conversation rather than seeing it as an attempt to shut them down, whether they might feel better about it. Also, I wonder how many of these mothers mentioned who only talk to their daughters about the neighbours' problems and seem disinterested in their own child actually then talk to the neighbour about their daughter? Obviously, none of this helps in the moment and it still feels crap to be on the receiving end of that kind of behaviour.... but sometimes, I had to grasp at what little glimmer of interest I could get from him or life would be too depressing.