I have the HP Elite X3 and i have the difficult problem.
Since 2019 i tryed put the smartphone to Mass Storage Mode with tutorials of xda-developers and i installing the Interop Tools App on X3, after installing the Interop Tools i can see the partition MainOS.
Now here is the problem, i renamed the archive bootarm.efi to bootarm.efi.old and i can't recovery the firmware because laptop's or PC's can't recognize the smartphone from usb, therefore the cell phone can show only HP Logo.
If i press power button or volume up or volume down, the smartphone turns off..
I need know the cheap jTAG or Tool Box for see inside the ROM partitions.