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The universe isn't infinitely old and the (observable) universe isn't infinitely big—which puts limits on the total number of galaxies and stars we can see.

Also, due to expansion (which causes a finite maximum distance as to how far we can see) many galaxies and stars are red-shifted and aren't observable in visible light (that's why e.g. the JWST uses infrared to observe distant galaxies!).

This thought experiment is called the Olbers' paradox: https://en.wikipedia.org/wiki/Olbers's_paradox