On Mac OS, in Safari, clicking on any of the download links not only downloads the zip file but incorrectly creates a directory by the name of the zip (without the zip) with the manifest.json, xxx.bin and xxx.dat components! Which is unusable!
It is necessary to control-click and choose “Download Linked File”
Also there exists a nRFconnect for iPhone IOS, currently web pages says to use nRFtoolbox, which does have DFU utility
Of course it’s not really productive to click on the download links from Mac OS in the first place!