Hi there! So, I've been through the "non-human protagonist" tag, and it doesn't really have much that interested me.

I'm looking for an alien or non-human protagonist in general (any genre really), but it'd be nice if it had them having to adjust to human customs. Some examples:

World Trigger
Laon
Heroic Age (kinda)
Karneval
Übel Blatt
Noblesse

Or something like Twink Twink that's just the daily lives of something/someone non-human, episodic kinda thing.

I'd prefer if it was a guy but I'm fine with whatever gender, but no romance-focused manga, please! ^^"
I'm sorry that it's so specific, but does anybody have anything for me?

Shinryaku! Ika Musume comes to mind, however the main character is a girl.
...and I think I might know some more but right now i can't think of any 🤢 ;;

Oh, The Devil Who Can't Fly (however I think the author is on hiatus right now T.T)

Maybe Parasyte -

The MC is human, but merges with a parasitic alien who lives in his hand. They have many disagreements due to their different values & the MC eventually starts to fear that he's losing his humanity. So it's more of a psychological conflict, with the MC and parasite not understanding each other's ideology, than a case of the alien having to learn how to shake hands or make coffee or anything.

Your request made me think first of Level E. I haven't read the manga, but the anime is very similar to what you ask.

The non-human protagonist tag isn't really exhaustive, you should also check things like aliens, robots, monsters, etc...

This includes mangas like Pluto, Yokohama Kaidashi Kikou, Doraemon, etc...