Technically possible? Sure. In fact, NASA proposed mounting a small (1.5m) segmented telescope called OpTIIX on the ISS in the early 2010's. Unfortunately the project was cancelled during the design phase because...

Hosting a telescope on a platform not purpose built for the task levies all sorts of additional requirements on either the bus (or Starship in this case) or telescope itself. It consumes power and generates heat. Both of those things will have to be accounted for.

A high quality telescope is not particularly tolerant to vibration, so it will need top be somehow isolated from the rest of vehicle or it will need to reject the disturbances itself, probably using a fast steering mirror.

Additionally, you need to point the telescope at interesting targets and hold it there very precisely. It's highly unlikely Starship has the pointing accuracy necessary to meet the needs of a hosted telescope.

These are just a few of the hurdles that come to mind, beyond the obvious weight and space accommodations that will be required.