I guess that you are not ready to try anything, not yet! And what you already tried is unknown to me (you are not sharing/asking much). Regarding reaching some conclusions: When you hold Vol+ (without any external cable being connected to the Librem 5 related port) and insert battery back into Librem 5, what is happening? Is it any LED light on? All we need is quite simple answer, either positive or negative.
Please answer my above question, as for now just leave below as still unknown territory:
This instructions are still valid: “Extract the downloaded JumpDrive release archive for the Librem 5, put the device into flash mode, then run the boot-purism-librem5.sh
script from the release” (that I already linked here somewhere). Just while sudo fdisk --list
step comes afterwards, and Librem 5 eMMC needs to be visible before starting with flash
procedure.
EDIT: @Flo127, this post should help you: New Post: Reflashing the Librem 5. Please go over few following ones as well.