@David-TP there are no "Unknown" devices in the list either.  Come to think of it, there are several iPhone devices in our family and I don't recall seeing any of them on the list, at least not recently.

The model number of my iPhone device is MLPF3B/A.

I've submitted a Deco APP log as suggested, with a link to this forum thread in the comment.

@David-TP Having submitted my APP logs I now seem to be in discussion with someone from support (I assume not you?)... is there anything you need or can help with?  I upgraded firmware to 1.6.3 Build 20230105 Rel. 30141 and now my own iPhone 13 shows on the client list, but still no other iPhone device (despite there being a couple of others connected... including an iPhone SE model no. MXD12B/A).

@David-TP 

I can confirm the following.  An iPhone SE in our household is completely invisible to Deco... i.e. nothing showing on the Client list, not even Unknown Device or anything like that.

But now disable "Private Wi-Fi Address" as follows:

Settings > Wi-Fi > info (i) button to right of connected network > disable Private Wi-Fi Address

The device is instantly recognised as a new connection onto the Client list, with a name matching that set in the device settings.

So it definitely seems to be this feature which is preventing devices from appearing on the list.

I could understand that maybe this is just an inevitable consequence of this feature, but we also have an iPhone 13 and iPhone 11 with "Private Wi-Fi Address" enabled, and both of these do show up on the Client list.

Any ideas?

@David-TP (or anyone)... no further insight on this?  Is there no solution or fix?  It doesn't seem ideal that there could be devices (possibly malicious) connected to our WiFi that we do not know anything about.  I appreciate that this privacy feature of iPhones makes it difficult, but surely the Deco network must know that these devices are connected (because these devices are using the WiFi network after all and traffic is being routed to and from them), so surely something can be displayed in the client list, even if it is "Unknown" or something like that... in my case I just see nothing at all!