I’m no expert in string theory but with all the bagging on string theory I tried to get to the guts of what's going on without as much "opinion". I did watch this great video which interviewed a bunch of scientists working on various aspects of string theory, and overwhelmingly it seems there's still a lot of interesting questions to be answered (even if string theory doesn't describe this universe), unfortunately I can't seem to find it at the moment.

I think the main thing is, even if string theory turns out not to describe reality, it shows that quantum mechanics and general relativity can be reconciled within a single, mathematically consistent framework. The tension between the two is gone and it's actually needed for physical correctness. Simply knowing that such a reconciliation is possible is already a meaningful result.

String theory emerged from attempts to quantize gravity. I think the most interesting thing is that when a relativistic string is quantized, a massless spin-2 particle inevitably appears in the spectrum. This particle behaves exactly like a graviton, meaning that gravity is not introduced by hand but instead arises naturally from the theory.

Competing approaches may possibly be all compatible, much like different interpretations of Quantum Physics.

The main difficulty with experimental tests is that the relevant energy scales and distances are far beyond what we can currently probe in the laboratory. This is not a weakness unique to string theory, but a general problem for any theory of quantum gravity. The Planck scale is simply too extreme to access directly with present technology.

As for experiments that depend on both quantum mechanics and general relativity, in principle these would involve situations where quantum coherence and strong gravitational effects are both important. Examples include black hole evaporation, aspects of early-universe cosmology, and possible quantum effects in curved spacetime. These are extraordinarily difficult to study experimentally, but they are what motivates the search for a theory of quantum gravity in the first place.