Anecdata: I’ve found USB powered external drives to be unreliable on the Pi, even when powering the Pi with an official power adapter. I’d recommend using an external drive that comes with its own power adapter.
I use a combination of official RPi 4 power supplies and an Anker 6-port USB power block that I'm pretty sure tops out at less than 3 amps.
More importantly, everything is plugged into APC UPSes.