https://arstechnica.com/gadgets/2022/02/64-bit-raspberry-pi-os-exits-beta-is-available-for-all-pi-3-4-and-zero-2-boards/

The Raspberry Pi hardware has included a 64-bit processor since the Pi 3 launched in early 2016, but the Raspberry Pi OS (formerly known as Raspbian) has remained primarily 32-bit. The Raspberry Pi Foundation has been testing a 64-bit version of the OS since 2020, though, and today the organization announced that the 64-bit version is leaving beta and is now a fully supported OS option on all 64-bit Pi hardware. This includes the Pi 3, Pi 4, Pi Zero 2 W, and all variants thereof.

The most significant benefit of the 64-bit switch will be software compatibility, since as the Pi Foundation notes, "many closed-source applications are only available for ARM64," and open source apps aren't always fully optimized for the instruction set that the 32-bit Pi OS uses.