On Mac computers, the USB-C to HDMI 2.1 8K Adapter outputs up to 4K at 60Hz. This is a limit in how macOS handles HDMI video output, not a fault with the adapter. Higher modes like 8K at 60Hz and 4K at 120Hz are available on compatible Windows PCs and other supported devices. If you are on a Mac and see a 60Hz cap, that is the expected maximum.