There's been some really interesting ideas for a new generation of telescopes that Starship's cargo capacity could enable. Telescopes on the far side of the moon are the classic example. They'd be shielded from the sun for 14 days out of 28, permanently shielded from Earth, and still have all the advantages of being in a vacuum. Gravitational-wave telescopes on the geologically-stable lunar surface are another interesting idea.

But I think my favourite idea is infrared scopes in the polar craters, some of the coldest places in the solar system. You don't need a complicated JWST-style extendable sun shield or limited helium supply. You are limited in terms of direction, but that's not a bad tradeoff.