HDMI 2.1 is a solid all-rounder with support for 4K at 120Hz, or 8K at 60Hz. HDMI 2.0b is a solid choice for 4K 60Hz, too, ...
Another tidbit from Apple’s support document: You can connect your iPhone to an HDMI display or TV with a USB-C to HDMI adapter or cable. Adapters and cables that support HDMI 2.0 can output video ...