In winbox, RB951 shows an active USB controller… I guess the port itself just isn’t attached to the board to keep cost lower???
Yes, if you would open the case, you would see that it lacks several required parts (and of course the port). Maybe in the future we will have a model that will have the USB port. Currently I can suggest the RB751U which does have it.
The quick guide does mention that the RB951-2n does have usb, so that should be removed from the PDF.
I have been using the RB951-2n as a bridged AP for a few days and it has been running very well using 5.18.