The Raspberry Pi 4 was supposed to support booting from a USB storage device. It wasn't until a year later official support is announced. It is still in beta but it is really easy to do, and from what I have seen it works really well.
You will need to install a beta firmware on your Raspberry Pi. This only applies to Raspberry Pi 4, the earlier versions already have support. You can read the official instructions on how to boot from a mass storage device on an earlier Raspberry Pi here.
Enable USB Boot on a Raspberry Pi 4
You first need to update your Pi, this includes the native packages as well as the Raspberry Pi additions.
sudo apt update
sudo apt dist-upgrade
sudo rpi-update
sudo reboot
After updating the packages and rebooting your Raspberry Pi, you need to install the beta firmware.
Edit the file /etc/default/rpi-eeprom-update and change the release from critical to beta. You can do this manually, or use this shortcut.
sudo sed -i 's/critical/beta/g' /etc/default/rpi-eeprom-update
Install the beta firmware
sudo rpi-eeprom-update -d -f /lib/firmware/raspberrypi/bootloader/beta/pieeprom-2020-05-15.bin
After it finishes, reboot your Pi with the following command.
sudo reboot
At this point you Raspberry Pi 4 will be configured to boot from a USB device. You can still use an SD device if you want to, but it will failover to a USB mass storage device if it does not find an SD card.
This is very similar to how it works on earlier Raspberry Pi devices except you need to use a beta firmware to enable support on the Raspberry Pi 4. This should change in the near future when support is added to the stable builds.
You can read more about the Raspberry Pi 4 Boot Loader Configuration here
This change will result in a huge performance boost as SD performance on the Raspberry Pi is atrocious.
