Build 21390 was often referred to by enthusiasts as part of the update—the codename for the major visual overhaul of Windows that eventually debuted as Windows 11. While Build 21390 was technically a Windows 10 build, it contained the DNA of the upcoming operating system. It served as a bridge, allowing Insiders to test backend changes that would soon power the new OS. As one reviewer noted, this build offered "a taste of things to come" regarding the future of Windows.
It marks the final chapter of the Windows 10 era and the prologue to a new one. For those willing to explore system internals, enjoy collecting rare versions, or need to run older hardware or software, the phrase "Windows 10 Insider Preview Build 21390 -x86 X64- ISO Incl" represents a potential treasure.