I'm a problem solver. I love solving problems, so trust me when I say that for some people, loneliness is an unsolvable problem.

The first step to finding a solution to any problem is defining it, because once you defined the problem state, you can also define the resolved state.
(i.e. coffee machine doesn't turn on -> coffee machine works normally).
But loneliness is a very subjective matter. What does loneliness mean for you?
Some people feel lonely outside a relationship, some people might feel lonely if they have nobody around that shares their interests, some might feel lonely because they're separated by age to their peers, etc. For some the most honest answer is "I don't know." This is not a matter of being too dumb to know, but rather the fact that some people have never experienced the contrast of not being lonely. Or more precisely they didn't or couldn't make memories of it when they did experienced it due to being preoccupied by traumatic events.
This makes this whole approach almost impossible, because while you can see the problem, you can't define it and therefore can't define a solution.

One of my teachers once said "The body builds upon stress". That's how we train our muscles, make our bones more dense or form new synapses. The thing here is that "loneliness" and "belonging" aren't abstract concepts, they are literally part of you physiology. Loneliness is a stress factor for your brain, and somebody who experiences it for prolonged and unregulated amounts of time will naturally build up a mental defense. But just as you can lose muscle mass, you can also lose you mental defenses. The issue is while you can train your body and mind mostly on you own, you can't do the same thing for finding belonging. By definition you can't belong on you own, which turns this from a simple problem to a complex one.

Another part of it is - things don't like being in limbo. To everything there's almost always a positive or a negative feedback loop. Depending on where on the spiral you started you either go upwards or downwards. In terms of loneliness this is often expressed as introvertism and extrovertism. While extrovertism doesn't make you immune to loneliness just as much as introvertism doesn't guarantee it, the former gives you a clear advantage of having more experiences that can break a negative downward cycle.

So if the stars align and a person has enough traumatic experiences at key points in their life, is introverted by nature and their life circumstances prevent them from breaking from a downward spiral the problem of loneliness becomes essentially impossible to solve. But this isn't a rare case, those stars align very often. The worst part of it is, that even if this problem is recognized on a broader scale as an "loneliness epidemic" the people on the far end of the bell curve of loneliness will most likely still not profit from any proposed solution. Because the solutions presented will be general solutions to subjective problems.

In short: loneliness sucks, and I wouldn't wish it upon my greatest enemies.