Raspberry Pi 4 can boot through USB, what enables you to use SSDs or NVMe drives through USB adapters to be used as storage instead of the MicroSD card. To enable that, follow the steps below.

sudo apt update
sudo apt full-upgrade
sudo rpi-update
sudo reboot
sudo rpi-eeprom-update -d -a
sudo raspi-config

In Raspberry config panel here are the steps:

[Boot Options]
[Boot ROM Version]
[Latest Use the latest version boot ROM software]
[Reset to Default] - [No]
[Boot ROM not reset to defaults] - [Ok]
[Boot Options]
[Boot Order]
[USB Boot]
[USB device is default boot device] - [Ok]
[Finish]
[Would you like to reboot now] - [Yes]

Back at the command prompt to make sure your USB drive is set to the default boot device:

vcgencmd bootloader_config

The last line should read: BOOT_ORDER=0xf41. If it says BOOT_ORDER=0x0, then you probably messed something up.

After finishing that, you can copy the microsd card image to the SSD to be able to boot from the USB on the next boot:

Open Accessories, select the app “SD Card Copier”.

• Copy from device is the mmc

• Copy to device is the USB device

After finishing up, turn off the Pi, remove the SD card, and boot again with the USB device attached.

(reference: https://www.youtube.com/watch?v=Hdg3Ptofzgo&feature=youtu.be)