I don't even think it's fraud. To charge someone with fraud, you have to prove that the person was harmed or suffered loss by the deceit.
If someone saw the face on IG, paid for the OnlyFans and got the porn with the same face as expected, have they been harmed?
I don't see how later figuring out the person doesn't exist in real life is considered criminally harming or damaging. You were never paying for the real life person by subscribing to the OnlyFans, you were paying for the digital content which you received. I can see why it would be disappointing, but I doubt a judge would consider that disappointment "harm" in a criminal sense as in real damage.
There are porn studios selling porn videos featuring people who don't exist in real life (dead pornstars) and that's not illegal.