If your Pi4B refuses to boot off USB, the trick is to write a boot loader that updates the eeprom to change the boot order. You can set it to boot USB, then fall back to SD, or vice versa. Even network boot.
To do this, install the Raspberry Pi Imager, choose Select OS, then scroll down to Misc Utility Images → Bootloader → USB Boot (or SD Card boot, whichever you need). Write the boot loader to an SD Card then boot the pi from it. If you have a screen attached, it should tell you when it’s done (I don’t actually know), otherwise if you’re booting headless, wait a few minutes, then power off the pi and remove the SD card. It should boot off USB now.