It's easy to explore QM and SR, because it's easy to accelerate fundamental particles to near the speed of light. Here's a video from 1962 where electrons were accelerated, they measure the time between passing two points (to get speed), and heat energy deposited on a target (to get kinetic energy) to show how SR works. Nothing QM specific, but shows how easy it is to get quantum particles moving that fast, so you can do experiments on them: https://www.youtube.com/watch?v=B0BOpiMQXQA

Combining gravity, which needs great mass, with QM, which needs small space scales, is "hard" to do in a lab.