When people say that, they're probably repeating what they heard and miscommunicating it. It means it can be made to run on a toaster or a super computer. -Not something a normie cares about.
If they're running KDE Plasma, ask them how to change the task bar size.
For Linux, it will very much depend on what OS you are using. On Mint you just right-click the bar, click "Panel Settings", and adjust the slider called panel setting.
Hell, depending on which version of Windows you are running, you might not be able to change the taskbar to the edge of the screen you would like, or change the size, without going into the Registry. That is something that normal people care about, and those same people should not be in the Registry.
Your submission in ""Linux is highly configurable"" was removed for being off topic.
Explaining how to change it, and comparing it to other operating systems, doesn't seem off-topic.
But this is your kingdom I suppose.