Can we experimentally understand the interior of a star?

[Phys12]

I have heard that whatever we know about stars experimentally is through only what we can see from its surface since the light from the interior is "hidden." However, when we look at the spectrum of a star, we do see absorption lines for heavy elements. I think the reason why that is is because when an electron of a heavy element's atom inside the star is excited and it falls back again, it emits a photon which can only be absorbed by an atom of the same element. And since there are no heavy elements (usually) in the outer shells of a star, the photon doesn't get absorbed and we see it in our detectors.

But if the latter part is true (we can see photons from inside of a star), then why is it said that the information from the interior of a star is hidden?

 

[Bandersnatch]

Inside the star, there are no atoms to excite, as all material is in the plasma state - which is opaque to light. The photons emitted in fusion reactions are fully thermalised by the time they make it to the outer layers.
The absorption lines we see are from whatever is found in the top layers of the star, where temperatures are low enough for free electrons and nuclei to recombine.

 

[Redbelly98]

Besides photons, neutrinos are also emitted in the interior of stars. And those pass through the outer layers of the star just fine. We experimentally detect neutrinos emitted in the interior of our sun. Not sure about detecting ones from other stars, the flux may be too low unless the star goes supernova.

 

[newjerseyrunner]

We can also see what's going on inside of the star with seismology. When we put our first high-res sun-watcher satellites up, scientists discovered that they were unable to resolve the surface of the sun no matter what they did. It took a while, but eventually they realized that it was distortion due to soundwaves. Once realizing that, we now had a mechanism to look inside the star: https://en.wikipedia.org/wiki/Helioseismology