Comment by Wowfunhappy

You're thinking of QuickTime 7, that can be optionally installed (as a separate app) even on macOS 10.14 Mojave! But the website is referring to versions of QuickTime X. QuickTime 10.2, which was included with Mountain Lion, was the last to support third-party components. (If you've ever used "Perian", that's what I'm referring to.)