I was in search of how to hide username in console for the sake of getting more beautiful screenshots.
I found fish_config that fish shell officially provides.
It has execellent web-based UI for us to configure color theme, prompt style and so on.

Just type in the terminal:

$ fish_config

Then your web browser will run and show the useful menus :)
With options, select one and click "Set ***", and it'll be done.

Besides, my current fish version is 3.0.2.

fish_config Web UI

colors

prompt

functions

variables

history

bindings

abbreviations

After changing "prompt", great, my console shows just "$" at the top of prompt lines:

Happy coding.