[giobox]

Officially there is no support for USB boot on Pi 4 yet.

The current supported solution is boot from read only file system on SD card, overlay file system with writes to the USB drive.

The foundation plan to add support back but for now only supported on Pi 3 and earlier.

[kingosticks]

You don't need to use an overlay filesystem (didn't know that was even a supported solution), you can move the rootfs to the usb device and point to it. See https://gist.github.com/lucabelluccini/9a11c48dcf1d627bbcbd8...

[destitude]

There is post that at least describes in detail how to enable this beta feature: https://www.jeffgeerling.com/blog/2020/im-booting-my-raspber...