Disclaimer: I could be wrong or not up to date, but this is my current understanding.
On the small scale, forces like electromagnetism and gravity pull things together much much faster than the rate of cosmological expansion. That’s why “we” don’t expand, and neither does our frame of reference. There’s a potential end to the universe where the rate of cosmological expansion (which increases over time) finally exceeds gravity and electromagnetism and eventually even the strong force, causing everything to fly apart forever.
Light waves propagate through spacetime itself, and basically it ends up being that there’s nothing pulling it back from expanding as the space it travels expands.