Linux 5.12 brings Intel Variable Rate Refresh (VRR/Adaptive-Sync), Radeon RX 6000 series overclocking support, mainline support for the Nintendo 64, the Sony PlayStation 5 DualSense controller driver, CXL 2.0 Type-3 memory device support, KFENCE, dynamic preemption capabilities, Clang link-time optimizations, laptop support improvements, and much more.
A decently sized release. My favourite is definitely adding N64 support to the kernel.