For extended objects like galaxies, a telescope can only make an image appear bigger, never brighter than naked eye.
I wish people would stop saying this! Yes, it is true in an important technical sense -- but that sense is not how most people use the word "bright" in everyday conversation.
By this argument, a 100-watt incandescent bulb is no brighter than a 60-watt bulb -- just bigger.
If you really feel that you need to make this point -- and it seems quite irrelevant to the original poster's question -- please use the word "surface brightness" rather than just plain "brightness," which has dozens of different technical and non-technical meanings. That will clue the reader that you're making a technical point, and he/she should not be surprised when the statement seems counter-intuitive.
Anyway, in answer to the original poster's question, many objects that appear extremely impressive through telescopes are completely invisible to the unaided eye.
The unasked question here is "Do galaxies look impressive in heavily light-polluted skies?" And the answer to that one is "no." They are impressive to the mind when you realize that you are viewing collections of billions of stars lying at unimaginable distances. But to see galaxies in detail -- to see their true beauty -- you need dark skies as well as a telescope.
The one exception with respect to needing a telescope is our own Milky Way Galaxy, which is very impressive indeed to the unaided eye from a dark location.
Edited by Tony Flanders, 08 April 2021 - 05:59 AM.