the double-slit experiment with gravitational waves had not been directly performed. Gravitational waves are ripples in the fabric of spacetime caused by the acceleration of massive objects. They were first directly detected in 2015, opening up a new field of research in gravitational wave astronomy.
The double-slit experiment has primarily been conducted with particles such as light, electrons, and even larger molecules. It investigates the wave-particle duality of these entities and the interference patterns that arise when waves pass through the slits. However, due to the extremely weak nature of gravitational waves and the technical challenges involved, directly applying the double-slit experiment to gravitational waves is currently beyond our experimental capabilities.
That being said, researchers have conducted analogous experiments to explore the wave-like properties of gravitational waves indirectly. For example, in 2017, a team of physicists used a Bose-Einstein condensate (a state of matter with wave-like properties) to simulate the behavior of gravitational waves. They observed wave interference patterns in the condensate, which provided insights into the wave nature of gravity.
It is important to note that scientific progress is ongoing, and new experiments and advancements may have been made since I'm not interested in that topic as much as i used to and my answer might be a bit outdated.