On May 2020, The Raspberry Pi Foundation released BETA version to support USB boot now, and this method has been tested.
For the details, please refer to Pi 4 Bootloader Configuration
Does the X825/X828/X829/X855/X856/X857/X862/X872/X835/X832 support USB boot?
Please refer to here: https://raspberrypiwiki.com/Does_the_X825/X855_support_USB_boot