Omarchy OS: How do I install Omarchy?

Download the official Omarchy ISO, write it to a USB drive, boot from it, and follow the installer.

Back up your files first. The installer offers a full-disk installation or installation into unallocated space. The full-disk choice erases the selected drive, and encryption is enabled by default. The official getting-started guide covers the current download, firmware settings, and installation choices.

Source: Omarchy manual.