Hi there,
So ok that’s a lot to unpack here. The uf2 file is drag and drop? file
You do understand that part right?
You put the device in bootloader mode it shows up as a drive and you drag the Uf2 file to it, Period. (it resets itself and reboots)
Are you doing that?
Have you looked (scanned) with BLE in Nrf_connect_for Desktop or the mobile App version? What is your mobile device. (old iphones) don’t do mesh for example, BTW 
Lots of folks on here working in the mesh stuff so Reply and others will also jump in to help. You using a dev board or Raw dogging it (chip only) 
HTH
GL 
PJ