While digging for electrical information I came across :

.63ma using HFINT or 1.58ma using HFXO ?
So I hunted down HFXO to see how to switch between them:

But nothing about selecting HFINT.
I found
The HFINT source will be used when HFCLK is requested and HFXO has not been started.
The HFXO is started by triggering the HFCLKSTART task and stopped using the HFCLKSTOP task. A HFCLKSTARTED event will be generated when the HFXO has started and its frequency is stable.
Searching this forum I found a reference to HFINT and starting HFXO but it was about the SDK for nRF5 products.
Where is the documentation for nRF9160 and I've been here https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.5.0/nrf/index.html and searched, there is nothing.