Is this app Icon Browser Safe/Legit?

I found it! It's an application called "Yad". As this is in the repositories, it has been checked by the good people at canonical and can probably be trusted.

There is an "Icon Browser" GUI utility (gtk3-icon-browser) comes from the gtk-3-examples package. If you have the same thing, then it should be fine.

To check it, first run the following command to find out whether gtk-3-examples is installed:

apt policy gtk-3-examples

If it's installed, run

gtk3-icon-browser

to launch the application. Associated .desktop launcher, viz. gtk3-icon-browser.desktop should be found in the /usr/share/applications/ directory.