The 64bit version of the Raspberry Pi OS is still in beta, however it’s possible to install it. Just follow along.
Install the Raspberry Pi Imager as explained here. Download the latest arm64 image from here and unzip the contained image file (.img). Open the Raspberry Pi Imager, click on Use custom and select the image file (.img). Hit Ctrl+Shift+X to specify advanced settings such as Wifi or SSH. Finally, click on WRITE.