Have you tried watching something like OddTaxi?
It's a bit social commentary (not very heavy but you can feel it). But I don't think it's about loneliness or relations much at all (I guess the Walrus and the Nurse Llama have a bit of a romantic fling but I don't consider it a major part of the show).
I'd say one of the major villains is someone who has fallen into the stereotypical gachapon gamer / whale / hikkomori type shut-in that sounds like you'd enjoy him as a villain.
So rather than catering to that demographic, OddTaxi skewers it by clearly marking that character as villainous.
It's just a solid Film Noir murder mystery, except the main character is the Taxi Driver with damn near perfect memory and facial recognition rather than a proper detective. It takes some time and discussions with various people around town to figure out the murder plot, but I was quite satisfied by it.
It's a dry show with a lot of talking. The bulk of the show is just the Walrus / Protagonist picking up customers around town, talking with them for 5 minutes and dropping them off.
But it's those discussions alone that leads him to the murder plot. It's really fun to see how everyone around town was so close to the murderer.
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I agree with you that there's a genre of anime that celebrates or dramatizes the Hikkomori / shut-in type (ex: Re:Zero, Jobless Reincarnation). But at this point, the Hikkomori is a stock character, just one tool to tell a story.
There's a lot of different uses of the "emotionally stunted Hikkomori" (ex: Anohana is the Hikkomori who through the drama of a Ghost coming back to talk with him, he gets pulled out of it and emotionally heals).
But anime and anime culture is above all, about stock characters that are borrowed, remixed, and turned into something new in the next story. The emotionally-stunted Hikkomori can become the hero in Re:Zero, the antagonist of OddTaxi, or a source of Comedy in Devil is a Part-Timer.
Frieren seems to cover a lot of Hikkomori Tropes (emotionally stunted character who is suddenly learning how to deal with emotions as she interacts with humans). So I think you're right in that she's seemingly related to the trope. I don't think I thought of her like that before but it seems to match up more-and-more that I think of it. She has all the markings of a Hikkomori in terms of attitude and even story progression (Himmel had to convince her to get up and try)