For consistency's sake, I suggest downloading a plethora of packages to make sure that all fonts are accounted for. Make sure to check every polybar config for the required fonts and install those fonts. Make sure that your terminal/environment supports ttf fonts and that your system has compositing. I used picom for my work, though I rarely configured it as I mostly use herbstluftwm, which overrides a lot of what happens with picom.
Make sure that you install Font Awesome 5!