general relativity is quite intuitive and most people understand how it works pretty well with the trampoline analogy. it's a simpler way to explain newton's laws in a mathematical framework. the problem is special realtivity is an attempt to use that framework to also describe superluminal and quantum phenomena, which is confusing, nonsensical, and doesn't describe how physical things work because it only attempts to describe things at speeds and scales that humans basically won't be able to manipulate for quite some time - it's theoretical. The problem is that special relativity was published first, the physical framework is based on the ontological framework.
so you have this framework presented as a singular unified concept that is riding on un-proveable assumptions that we're assuming we're going to discover in the future... and we're supposed to take its general ease of use and apparent but untested correctness as the justification for why the framework is correct? I hate to say this but there is no wave function collapse. we made that idea up to explain something confusing - that's not reality, that's a framework to describe a simulacrum of reality that works most of the time.
Eh, the trampoline analogy is a very, very simplified way of explaining how curved spacetime is gravity. Actual General Relativity isn't intuitive at all. And it has all the reference frame stuff from Special Relativity, except it goes a step further and adds acceleration and spacetime tensors. Neither have anything to do with quantum phenomena.
Alright, I gotta clear some shit up here.
Special Relativity describes the physics of inertial frames at very high speeds close to the speed of light. Inertial meaning that they do not change their velocity/direction. General Relativity, well, generalizes this to accelerating reference frames and particularly gives a description of gravity. Where Special Relativity is mostly about the transformation of frames of references and how the fact that the speed of light is the same in all of them leads to weird shit, General Relativity introduces a whole new way of describing space itself. Gravity is a result of spacetime being curved, and mass curving spacetime. Special Relativity was published first because it's the simpler part, and started by the works of Lorentz and Poincare, nothing quite ontological about it.
Neither actually allows superluminal movement (as in, faster than the speed of light in vacuum) per se, although one can in principle use speeds faster than the speed of light (just not exactly the speed of light) if there are imaginary masses. Which are maybe mathematically valid, but never observed.
Quantum mechanics describes very small, low energy physics. The opposite of what Relativity does.
Relativity and quantum mechanics are also fundamentally incommensurate. It's actually the big task in physics to eventually unify relativity and quantum mechanics, because right now they don't work together. They're entirely different theories working on very different areas, even the math is very different. There is quantum electrodynamics, which is the application of special relativity to quantum mechanics, but the big deal about General Relativity is its description of spacetime as a field and gravity as a property of that, and so far nobody has worked out a working quantum gravity model.
And yes, Special and General Relativity have predictions that are observable. So does quantum mechanics. Some examples:
Special Relativity: Particle accelerator experiments show time dilation. Muons accelerated to very high speeds have a longer half life compared to muons in the lab system, also cosmic particles measured on Earth display length contraction.
General Relativity: Gravitational lensing has been observed, General Relativity has also been observed with various atomic clock experiments and the Mercury orbit anomaly.
Quantum mechanics: The whole weirdness about observers affecting outcomes and wave functions has been shown in double slit experiments. With photons and even large molecules like C60 "Buckyballs". Quantization of energy states is also fundamental to how lasers work, and quantum numbers are used in things like NMR machines and many other applications. The tunnel effect, very much a demonstration of quantum mechanical probability, is used in tunnel electron microscopy.
And many more for each.
Basically, individually these theories work and describe what we observe very well. But we don't know why shit is like it is. Schrödinger came up with his equation kinda out of nowhere and it turned out to work. Only later did someone derive it properly.