Why doesn’t DH express an opinion about anything?

If thats genuinely how he feels, thats really sad.
Has he given you examples so you can understand how he has come to feel this way?

Is he generally dismissed? If you say no, why does he think he is ?

I think there are probably plenty of men who aren’t really bothered much about home decor, as long as it’s not something they hate (not mine - he cares more about tiles than I do!)

Ask him what are the things that matter to him that he’s like his opinion heard on, then make sure you listen.

Poor man lost the motivation to live.

You do have marriage problems OP and they will get worse and worse. You're DH has already checked out from offering opinions and sooner or later will check out from pretty much all family life in order not to rock the boat (whether thats true or not).

I remember a post here a year ago where someone was blasting their DH for being totally useless for not being able to cut a birthday cake without asking them first how they wanted it cut. This is going to be you in a few years OP as your DH won't do anything without checking in with you first.

I sat in a team meeting a few years ago where a few people spoke and then they asked someone else to share what they thought and they said "I don't see the point as whenever I say something you disagree with it'. The reply from the louder people was of course not to which they replied 'See, you even disagreed with that'. It was an exchange that still haunts me today how some people see themselves.

You want your husbands opinion?

I tell mine whats happening and thats it 🤣 "im painting the lounge this colour do you like it?"
"No"
"Youll get used to it"
Then when its done he says its not as as he thought itd be.

Is interior design of any interest to him? It’s of no interest to me, I haven’t really changed anything since I bought my house and when k have had to I typically just went with whatever was on offer or something recommended by someone else, if someone else has made a decision I’d be thankful and wouldn’t be offering an opinion just for the sake of it. If he doesn’t really care and he knows you have a preference why would he bother giving an opinion?

My DP can be like this by default: he was brought up by an abusive grandfather and a mother who had serious mental health problems and he grew up to associate expressing opinions with fear. He was routinely insulted and sometimes physically attacked for expressing opinions which conflicted with his grandfather’s views so he learned to keep his mouth shut.

He has over time become more willing to express himself but it goes against the grain and isn’t easy.

I think a lot of people are raised to believe that having opinions is rude and antisocial or to associate it with conflict, so they go out of their way to avoid being direct about their views. It’s very hard to shift once this becomes internalised.

Hard to say. Do you spend a lot of time sending him things and asking him about things that he has no interest in? Do you do it because you feel like you should, and because you want him to take an interest?

If he genuinely doesn't mind (in an 'equally happy with either' way) whether you have green or blue curtains, or whether you go to France or Spain on holiday, then tbh if I were you I'd just be quite happy to get to choose myself! If it were over something like a financial matter, or which school to send your children to, then I'd expect input. Repeatedly badgering him for an opinion he doesn't want to give, and then shutting down his opinion (if that's what you're doing) would be enough to discourage most people tbh.

Whilst some debating can be good...if you know you're never going to win or be listened to then it gets boring. I know someone who thinks they like to debate, but really just likes the sound of their own voice and don't listen to anyone else's view or opinion.
Not saying the OP doesn't listen, but we just don't know. I think really the OP needs to reflect and then have a proper talk with DH.

My DH is like this, he generally assumes I have a stronger opinion than him on everything, especially concerning the house, food or kids. I'm actually not very opinionated myself, I just fall into thinking I have to make decisions because he doesn't. I now make a point of saying I would like to know what he thinks before I express my opinion, or if he really has no opinion at all, push him to choose between two or three things I like - and crucially actually accept his choice without questioning it. It's important to me that I'm not carrying all the decision-making responsibility, but maybe you're actually comfortable with being the one making the decisions and he's fine taking a back seat? If it works for you both and hasn't caused an issue all these years, maybe it's not a problem?

I asked him directly why he didn’t offer any view on anything, and he replied he’d come to realise that his view was generally dismissed, and most things aren’t something he has a strong enough opinion about to get into a disagreement.

Does he have a point?

I wouldn’t say either is in the wrong here. From what I can see he feels you dismiss him and counteract anything he does say so he doesn’t bother. But in your defence it’s good to chat and debate rather than just always agreeing or you would never be able to have back and fourth conversations. It sounds like he could be a bit depressed or something.
I would explain to him that him saying this has made you question a lot, and made you feel uncomfortable, that you want more from him and assure him you won’t bite his head off if he doesn’t agree with you (not saying you do but by saying that it may reassure him if that’s what he’s thinking).
How old is your DD? I know quite often men can become a bit withdrawn during the younger harder years and it’s often not spoken about a lot. It’s good you’re wanting to sort this out.

I was genuinely shocked as we get along fine, no issues with the marriage.

Because, as he says, he doesn't risk disagreement by offering opinions.

I think it's hard to judge without knowing the background.
When he has expressed opinions in the past did you listen and go with them? Or did you express a different opinion and end up going with your suggestion?

he replied he’d come to realise that his view was generally dismissed, and most things aren’t something he has a strong enough opinion about to get into a disagreement

You seem to have answered your own question here.