How do I hide a non-visual component on a form at design-time?

A rather drastic measure would be to upgrade to Delphi 10 Seattle (or later) as this is one of the new features that Embarcadero have added. There is a small button next to "Toggle Form/Unit" called "Show/Hide Non-Visual Components" - the shortcut is CTRL+H

This option is included inside of the Gexperts menu and is called Hide/Show Non-Visual.