bladerunner 2049

It’s a futuristic sci fi movie so it might not be what you’re looking for. Loneliness and alienation are central themes, though

Moon

Eternal Sunshine of the Spotless Mind. Explore how it feels when you deliberately choose to lose a relationship.

Pi

The main character is an unemployed mathematician with schizoid personality disorder whose social interactions are mostly with his old professor and the people in his apartment building. The movie is a thriller, but the main character's isolation from the rest of the world is rather stark. This is helped by the fact that it was filmed in high-contrast black and white.

I can set up a camcorder if you'd like

It's been a while since I've seen it but Cast Away is about being stranded all alone and dealing with loneliness. I have a feeling this isn't what you had in mind.

The Perks of Being a Wallflower is one of my favorite movies. Although he's not without friends the entire movie, I think you might still appreciate it.

The new Joker movie is definitely worth the mention. Although depressing, I really appreciated the movie. It's not actually a superhero movie in case that's deterring you from watching it.

Although I haven't seen it yet, Lost In Translation is near the top of my watchlist. It might be up your alley.

Edward Scissorhands?

Moon - Sam Rockwell lives alone on the moon.

Welcome to NHK is anime about a NEET. He ends up finding some kind of friends througout the show tho.

Also what you're describing is basically the concept of a doomer.

I am a doomer

Maybe not quite what you're looking for but Tom Hanks in "A Man Called Otto" might float your boat.

Does being lonely due to war and it's trauma count? If yes, I can highly recommend old soviet movie Come and See - https://www.imdb.com/title/tt0091251/ Just don't get discouraged by country of origin, it has no effect on the movie.

Oh I have something for you!

I just watched Beau is Afraid, https://m.imdb.com/title/tt13521006/ and it was epic. One of the best movies I've seen in a long time.

I would rate this as 7.5 and really don't agree with the lower imdb rating here.

Taxi Driver

Stranger Than Fiction. Well, Harold does have his wrist watch for a friend, but he doesn’t know it.

"A Silent Voice" (anime movie) is my go-to when I want to feel profound emotions, even if it's crying about the fact that all my friends are hundreds of miles away or dead now and I apparently forgot how to make new ones.

So this is a bit special. It’s very very low budget, awesome and free: Pretend That You Love Me

I don't seem to recollect any movie at the moment but here are some TV shows or anime -

1. Mr. Robot - one of my favourite TV shows, most people using lemmy might have already watched it.

2. Boku no Kokoro no Yabai Yatsu - its about a very lonely middleschool kid's romance

3. Koe no Katachi - very popular anime movie. Also one of my favourites.

4. Bocchi the Rock - Anime about an extremly introverted girl wanting to play guitar in a highschool band.

5. Re-Life - its an anime about a grown up guy getting a chance to re-live his high-school days as part of a experiment or something like that. It was pretty good.

6. Lookism - its a Manhwa, but also has an anime. Basically the main character gets 2 bodies mysteriously. The original body is the ugly one which people bully him for and the second body is like that of a (male) kpop artist which people view differently.

7. Death's game - it's a kdrama I recently watched. Although it doesn't exactly fit in with the theme of 'lonlieness' I thought I'd mention it.

P.S - some shows I mentioned here might not be as loneliness inducing as you think.

Donnie Darko

Schultze Gets the Blues

There is a great list here.

Also Wild Strawberries (1957).

Home Alone, hehe

Night on Earth (1991), taxi drivers & passengers meet temporarily. Nobody's happy.

Wit, about a professor of English lit going through cancer treatment basically alone.

Station Agent

Seeking a Friend for the End of the World

Swiss Army Man.

Not sure if it's exactly what you're after, but "Buffalo '66" checks the dark and lonely boxes pretty thoroughly.

The Hunt is a great one but it's about losing your friends and their trust, after a misunderstanding. Be prepared to shed a few fears

The Bothersome Man (Norwegian: Den brysomme mannen)