You see people don't write that at all(They do but rarely) and as a result "reincarnated as a mob" has become the new cliche with how many stories are with this one trope
Most fiction where the MC claims to be a villain, mob, NPC, or even cannon fodder is 'stupid' enough to not realize that they are the protagonist in their own life story.
I think its would be pretty interesting to see a normal, say high schooler, suddenly finding themselves as the protagonist and facing the responsibility of being a hero
THIS IS WHY i want to see a MC=Protag !!!
Im tired to see "oh crap what i should do ! I better prepare everything before protag appearance ! And for some reason the heroines are attracted to me!" nonsense bc MC=Mob/Villain.
Not that i want a dense/dislikeable-useless MC being scared of hero responsibilities. (jps bad at writing them)
But I want to see a "normal" person => hero.
Reincarnated/Becoming the hero was the phase from 10+ years ago
It was mass produced slop that people became tired of, which is why it became reincarnated into the mob afterward
If you think about it something like SAO fits your criteria.
In this particular case i speak of is : Oh i transmigrate into some kind of (original) series/book and become the random no-name mob or villain(ess)
Bakarina and co.