To use ESPHome Device Builder in Chrome on Arch Linux, don't forget to add your user to the uucp group and reboot.

Or do this without rebooting:

sudo usermod -a -G uucp username
newgrp uucp
chromium

Then holding down the flash button (right of usb-c) while plugging in and continuing to hold the flash button while starting the flash process by pressing "Prepare for first use" from https://web.esphome.io/