For anyone who may not have noticed, Raspberry Pi Org have finally introduced native USB booting option on RPi 4B, excellent third party video on implementation available here:
https://www.youtube.com/watch?v=2zrwjGcyM5sUSB booting work arounds were available for the RPi 4B and earlier 3B/3B+ models but were quite involved and most still required an SD card as well as a suitable USB device.
Note, the bootloader FW change required is still a beta release, warnings are issued in the video.
Have tried out on a RPi4B, 2Gb. RAM version with a 120Gb. SSD & USB-3 SATA adaptor, works very well using the latest available bootloader beta FW dated 15/06/20.
One thing I noticed, if running with both SD & SSD connected, any changes made such as re-naming etc. appear to be implemented on the SD card only, absolutely no reason to have an SD card inserted of course, just an experiment to see if this would still boot.
I think this would work with a RPi 3B+ or even a RPi 3B running on the new Raspberry Pi OS which is currently just modified Raspbian Buster, have not tried either model as yet.
Will certainly make RPi projects such as a NAS, VPN etc. a lot easier to set up.