I searched for "microsoft core fonts" in the Kubuntu Software Center on my laptop and the search turned up no results.

Instead, I just installed the microsoft core fonts from a terminal like this:

sudo apt install msttcorefonts

That's all there is to it. You'll have to agree to an EULA to use the fonts, but other than pasting that command into a terminal and entering your sudo password, there's nothing more you need to do to get the Microsoft core fonts installed on your Ubuntu or Ubuntu derivative system.