The last time Apple gave macOS a fresh design was in 2020's macOS 11 Big Sur.
That release was relatively light on new features and heavy on symbolism. Big Sur is also when Apple finally jettisoned the "10" in Mac OS X after two decades. More importantly, it was the first release installed on then-new Apple Silicon Macs, the culmination of a decade-plus of in-house chip design that began with single-core, low-power iPhone and iPad chips and culminated in something powerful enough for the Mac Pro.
Today's macOS 26 Tahoe release holds up a translucent, glassy mirror to the Big Sur update. It comes with an all-new look, one that further unifies Apple's design language across all its operating systems. And it even throws out the old version numbering system and introduces a new one.