@PM490 - I just tried the libcamera-still command on my RP3 both on my RP4 as well as on my RP3, and it failed exactly like you described. Maybe I had the tuning file somewhere in my path when I tried it previously? I have no idea. Anyway, you already described a way to use it: either copy it from the default location to the directory you are calling libcamera-still from, or include the full path in order to make it work, like so:
libcamera-still -o new.jpg --tuning-file=/usr/share/libcamera/ipa/raspberrypi/imx477_scientific.json
Thanks for bringing this to my attention!