Yes, JLink is essential for this level of testing. I generally use the “Debug with Ozone” option.
I could help you if using a XIAO MG24 but unfortunately my “expertise” doesn’t include the NRF range of devices. I have used them and have a range of devices and development kits but find the development process a little “daunting”.
A few of us are currently “struggling” with the NRF54L15 development (I would like to use for Matter and Zigbee products).
Good luck with the “recovery” 