Have you ever met someone who is able to deeply engage in conversation in a wholesome and detailed way?

Yes.
I have a friend who is extremely intelligent, endlessly curious and was raised in a locally well-established and notoriously generous and civic-minded family. So he was raised in that milieu of sincere kindness and generosity, and whenever he's come across anything that interests him (which is seemingly something new every week) he seriously researches it until he understands it.
So it pretty much doesnt matter what the topic is - he knows something about it, but his personality has been shaped so that he's attentive and considerate rather than pedantic and self-absorbed. I've lost track of the number of times I've seen him engage in obviously mutually enjoyable conversations with complete strangers over... pretty much anything.
I vacillate between thinking that it's remarkable that he's the way he is and that it's remarkable, in a different sense, that that's so uncommon.
- Some of it might be age. I didn't realize until recently what I wanted. Got a new co worker who's only a couple years older than me (I'm 46) and after a few days of working with her, I told her she's ruining my other friendships because I've realized how boring many of my friends are. She's just very easy to talk to and we can cover tons of subjects. We always have something to talk about.
  I don't think you can expect someone in their 20s to really know enough about enough things to really be euradite about much. They also don't have as much experience talking with people to be remarkably eloquent. That's not to say that everyone younger than me isn't worth talking to, but maybe you're scouting in the farm league and don't know it. Keep talking to everyone though: one day you'll find someone you hope never stops talking to you.

I've met a few.
What I've noticed is they rarely use the words "I" and "me". They rarely talk about themselves, which is bloody unusual. I try to follow that example.
This whole comment is a failure of that philosophy. My bad.
- my bad
  Bad*

No
- Okay

I’ve met tons of these people. I think it’s sad the rarity this question presupposes. People like this are all over the place.
- Any conversation that really makes you think
  
  Which is all of them if you approach them right.

In technical fields? All the time. It is super rare for someone to ignore your arguments or resort insulting you during a discussion.
- Good for you if that's your experience, but I cannot say the same. The difference I found is with the way those people ignore arguments and insult you.
  I can talk to a person from a technical field and come out of that conversation feeling like shit because I was called all kinds of stupid indirectly.

I know a woman who makes a point of telling her husband about her day, whether it was good or not. She talks about her hopes for tomorrow, and for days more distant in the future. She genuinely wants to know more about other people, and is really interested, and she is great at talking to people and making them feel important and unique.
The only part that is confusing to me, is that I am her husband. This vibrant and compassionate woman went and got hitched to little me, it's been 14 years, and I don't know why she stays.
But I'm glad she does.

Yes, I literally teach classes on how to do this, and why it's hard
- I struggle to get basic thoughts out of my head and into words. Do you teach this class online? I'd be interested in looking into it.
  
  We do deliver the course online
  Is there a DM option on Lemmy? Happy to send you a link but don't want to be advertising on here.
- Do you have any preferred references, or past lectures on this topic? It sounds very interesting
  
  It turns out the trick isn't talking, but listening.
  
  There's an abundance of material to study, I'd suggest starting here. https://books.google.com/books/about/Counselling_Skills_and_Theory_5th_Editio.html?id=ua9VEAAAQBAJ

Yes, and I think I learned, in general, how to focus on anything by observing them do it. She was my first major, unattainable, love. She was just zeroed in, always, and I knew I had to learn the skill. I still can't do it to the level she does, but it's a remarkable skill to work on. Even at amateur levels, it's extremely useful.

Absolutely! And I'm finally gonna marry her in less than 2 months.

Yes), there is people like that, they usually are unpopular because they don't try to gain standing in society but instead enjoying what they do, they are very chill and wholesome, you see, society as a whole is quite egocentric even if they try to virtue signalling, people wrestling each other socially, and if you want to find people like that, then you need to step outside from the rat race, then you will see that there are alot of these type of people, they are actually all over the place)

Yes, and a lot of people but hardly straight off the bat. It takes a few rounds of small talk before engaging in something meaningful. In my experience, the more creative the person, the faster they will engage in a meaningful conversation, with musicians probably being the fastest ones.

Yes, I few people.
An old classmate of mine was fascinated about space and space exploration and could go on and on about it. It never was uninteresting to listen to.
Also a friend of mine. He's a pretty smart guy and has opinions on a lot of things. He also knows a lot of things about different topics. We can talk about anything and it will be an engaging conversation. I love that guy.

I have met people who are able to do this, and believe that everyone can, already or eventually. Unfortunately though their willingness to do it with me never aligns, so I don't get to do this much.

Yes, but only other autists.

What is a deep conversation? I am not the most socially adept fella so if someone could clarify this would be much appreciated. My best guess is that its asking about the very personal details of someones life.
- Deep engagement in a conversation and a deep conversation are different things I'd say.
  Deep engagement to me is when someone starts thinking about your position as their own. One time I asked a store clerk where I can get a shovel in the store. They didn't have any, but he kept brainstorming with me what I can use as a makeshift shovel or where else I can go to shop for one. It was very engaging and nice to be part of.
  One way I can describe a deep conversation is a topic that, when someone starts getting into it, the socialized knee-jerk reaction is to insult them to shut them up (unless you happen to be impassioned about it as well). Think sitcom: some quirky character waxes poetic and the others tell them to can it because the plot must go on.
  I guess a deep conversation can be a personal one, although I would maybe categorize that as an intimate conversation rather than deep. Both are conversations that people usually just to ignore, avoid, or tell others to stop because they want to get on with their own lives. Usually deep conversation topics are larger-than-daily-life topics, so that's probably why

Yes - the fam

I have met few people that can even accept my experience without trying to twist it into their own.
- My experience is that people who try to "twist it into their own" are really just trying to make a connection or keep the conversation going. I try not to fault people who do this a bit too much. Often, they are doing their best to navigate life like everyone else is.

No idea, I'm not capable so I'm not sure I have a test for this...

Yeah