To think DH should have told me he sold this car

Well, depends. The car was destined for sale, you were away and your husband very competently managed to complete a sale without supervision or getting you involved in any shape or form. I would consider myself quite lucky there wasn't one more admin thing for me to worry about.
In fact, similar thing happened to me just a couple of weeks ago. I knew the car was going to be sold, I came home after two weeks of seeing my family and didn't find it on a drive. I immediately assumed the car was sold in my absence and, what do you know.. it has!

Christ, I’d be bloody thrilled if my husband could handle something like of his own accord. He can’t fart without some help from me!!!

Oh my gosh! Honesly I would have had a bit of a laugh with him. Told him I had called the police and they were here now!
You seem to be worrying over something trivial that is over.
Do you think there is a deeper issue? I wondered if this is why he was sending trivial messages to cheer you up? Or is it that you are a little bit controlling and he thought he may get get aggro?

You know that age old saying? If it's not going to matter in 5 years/months/weeks time then don't spend 5 minutes posting on Mumsnet about it.
Well, that.

Is it only me who is wondering why you are buying your daughter all these cars?! 😂

Sometimes cars sell very fast, I sold one on Facebook in about half an hour once! It probably all just happened very fast and he forgot to mention it to you if he wasn't messaging you at that particular time!
I wouldn't overthink it ☺️ you had a weekend away and came back 4k richer with no admin work done. Winner winner 🤑

Well yes of course I'd ask him but I wouldn't get the arse that he forgot to tell me and feel the need to post about it

Have you read the thread?

Of course I have.

She has simply asked on a forum if people think it's strange to not mention selling a big item to your wife.

And several people have said “Not really - he just forgot to message you”. Selling the car without telling her he even planned to - yes, that would be weird. But they’ve been planning to for the last month.

These forums are to ask questions and get people's opinions.

And I have and several others have offered opinions. They just happen to be different opinions to yours.

At what point has she made an issue of it or acted like it was such a big issue? Have you read the thread? OP says she asked him about it, he replied, he apologised for not mentioning and OP accepted with no hard feelings. She has simply asked on a forum if people think it's strange to not mention selling a big item to your wife. These forums are to ask questions and get people's opinions.

I think this too.

Well obviously you disagree with me, but I don’t think it’s “silly” to tell the OP she’s making too much of it. I would think someone was hard work if they were still acting like a simple mistake was such a big issue!

He forgot to tell you, and apologised for forgetting. You'd already agreed between you you would be selling it. There's no issue here

I'd message him to ask if he'd moved it and when he replied no, he'd sold it as we were trying to do, I'd say 'Oh, right, it gave me a bit of a moment when I saw it was gone - do you want rice or pasta tonight?' and get on with my day.

I was going to say something similar. As a widow I've just had to sell my rather old car, find another rather old car and deal with all the paperwork etc. It would've been bliss to have someone just take care of it all and £4,500 in the bank to boot.

I said the OP was getting some silly responses, you tried to shut it down saying people are not saying whatever, they are saying blah blah. So I pointed out all the comments of people being silly to the OP.

I was referring to the poster I quoted, not you OP.

What do you want me to do, reply to every single post? Even the OP isn’t doing that!

So you're just picking out the messages you want to, not the ones that say:

You're hard work
You're determined to make it a big deal
You have issues
Why are you running to a public forum

Has anyone actually said that they wouldn’t expect a message about it? Or is it actually that people are saying, “Yeah, he should have messaged but he forgot; no harm done”?

It's not the wondering where it was that people find odd. It's the fact that once your DH had told you where it was and apologised, that you are still thinking about it. Other than about how to spend the money.

This

Are you asking would I see the car had gone and just shrug my shoulders? Well no, I wouldn’t, and I don’t think anyone is suggesting you should have. But I’d do exactly what you did and ring up and check. I’d probably think my husband was a bit daft for forgetting to mention it, but once I knew that’s what had happened, that would be it - “mystery” solved.

You even said yourself that you sometimes move it to avoid it looking abandoned. That was another fairly likely explanation. A car you wanted to sell is sold; why are you making it into an issue?