It's not terribly difficult; very few of my characters fit that bill. And Katniss isn't orphaned; she's disadvantaged, but she's fighting to defend her family rather than having nothing left to lose. A better example would be Lessa of Pern, who does fit the mould you're talking about in Anne McCaffrey's Dragonflight. My own work is based on a similar story, albeit more alt-hist adventure than fantasy, but I changed the parameters so I didn't fall into the same groove.

Basically, a child raised with two loving parents in a decent household needs some conflict or drama to get them out of that situation. So in creating a conflict, you might go for something which doesn't involve a young person trying to prove themselves to other people, but try creating a character who has their own established life and following a plotline which involves their own concerns. Perdido Street Station is basically about a xenobiologist who is given an interesting assignment which drags him deeper and deeper into the politics of the city. Many AD&D books feature adult characters whose adventure comes simply from being in the right (or wrong) place at the right (or wrong) time.

My protag is such a protag, but then I set the main books during his twenties, when he bites off more than he can chew as a lawyer and gets himself into big trouble very quickly. Outside the main series, my characters also often act as detectives taking on the challenge of figuring out a mystery or engaging with someone who is up to no good: they are presented with the mystery or situation at hand rather than being forced out into the big-bad-world by a strange mentor with a big destiny for them. There are poverty-stricken characters involved, but I tend to write about adults with their own agency: a character of mine who was the protagonist of a short novelette I wrote has fallen on hard times and is mainly the protag because he dares to answer back when spoken to condescendingly. The only orphan was, again, an older teenager, already an apprentice, but who joined up as a soldier to see the world only to find himself in a frustratingly menial position in a hospital. Him being an orphan is tangential, and mainly because I didn't want him to have too many ties to his home town and just be frustrated from a lack of adventure in his life and a war going on around him rather than deeply personal motivations.

Basically, you're thinking of one single plotline that is possible for a fantasy book to take, and which forms a lot of literature for children and teenagers. Literature does fall into a lot of different forms. I tried to think outside the mould in general because I didn't just want a book which travelled across the map and back again, so I tried to find an alternative way in. I think what you might do at this point is to read a bit more widely - try to find books which aren't stereotypical/archetypal fantasy and maybe go outside the genre itself.