Only few pieces left (somewhat complicated device but worth every cent). Supports two charging modes (works preferably with QC2.0 or even with QC3.0 but there is switch to PC-F mode and that one supports DCP coding − sometimes the one that should be preferred. But what is sure with this device? That its manual needs to be reread several times (otherwise might turn out as it is another, regular one). Charges PinePhone battery with just over 1.6A (4.53V with my current setup) in DCP coding, both setups same wattage. In PC-F mode setup, Qualcomm® Snapdragon 845 phone with removable battery currently charges from 24% with 4.57V/1.42A, DCP coding, and this current is well under what would be speedy charging wattage when QC3.0 protocol used (as and when normally negotiated). And anyway, in AUTO mode, this USB-A to USB-C cable will switch to green LED light (charging stopped/disabled) when your Android smartphone battery full.
Please note that above device (and cable at the same time) is not related to Librem 5, as not needed there.
I’ve have had the same thought (please understand and comply with your main processor charging requirement, coding or protocol, at first place, before trying to reduce some/any charging amperage, also note it is just me and therefore the one that do not think that charging over USB port from some laptop helps any and certainly not big to prolong connected smartphone battery life), therefore (sounds strange to rely on some cable but good starting point to preserve/prolong some battery life) my link above:
P.S. Only comparable cable to the above one would be: Charby Sense Auto Disconnect Cable with its switch-button to DCP coding, but not available as USB-C any more (its Charcol Sense would be the almost useless one or rather far away from my expectations).