The idea that aliens might be using black holes as quantum computers is speculative and not supported by any direct evidence.
However, some physicists have proposed that a highly advanced civilization could use the properties of black holes to perform computational tasks that are beyond the capabilities of traditional computers.
The concept of "black hole complementarity" suggests that an observer outside a black hole and an observer inside a black hole would have different but complementary views of the same physical system. Some physicists have proposed that a civilization could use a network of black holes to perform quantum computations by taking advantage of blackholes' unique properties.
However, this is a highly speculative idea that is not supported by any direct observations or evidence at this time. While the idea of using black holes as quantum computers is intriguing, it is still theoretical speculation rather than a confirmed scientific finding.