Thinking about the ideas of space and time in einstein’s general theory of relativity, how do we explain the fact that all galaxies outside our local group of galaxies show a redshift?

Due to the gravity

Explanation:

Since in space outside of our galaxies, it exists bigger starts than the ones around us, that means that they had bigger gravitational forces. so the wavelength of the electromagnetic radiation that they can emitted climbs out of their gravitational force. With an increase in wavelength of photon, it moves until the red end part of the electromagnetic spectrum, in this order, get the name of redshift.

this would be about 43%