If you're referring to relics in the Catholic sense of the remains or possessions of canonized saints being "fake" then there's probably an element of truth to many (most? not sure...) in that they likely were at a time fabricated. However, this core belief in them being real and the history surrounding them still makes them historically significant so it's hard to understand what value there is in claiming them as fake in this context. Is the Shroud of Turin the real shroud used to wrap Jesus at his burial? Pretty much certainly not. That said, it is still clearly historically significant.

Now, if more broadly you are referring to relics in the generic sense of objects of historical importance surviving from times long ago, then it seems obvious that most Christian relics are NOT fakes. Christianity has a long, deep history that has influenced the creation of massive amounts of art, literature, architecture, pottery, etc.