I beleive that this is the very direct store from AENZR:
Please test it with this old school 5V/3A PD complaint power supply: https://www.artwizz.com/en/smartphone-accessories/technics/powerplug-usb-c-cable_28424_15853/ (one of my favorites). As yesterday introduced here: USB-DCP-5V-1.5A protocol and Librem 5 - #16 by Quarnero.
EDIT: Both linked Artwizz 5V/3.0A boot up Librem 5, when its provided battery not inserted (without any additional firmware upgrade). Meaning without:
And as kindly, closely and directly related: