My iPhone 13 PM on 16.0.2 will not forget the old wifi networks from our previous house.

There is no longer a ‘Forget this network’ option under the Other Networks listing. To get that back you actually have to log in to a network that you do not have any more….!

Then you get the Forget option again.

Then you use the Forget option.

Then you find the network you told it to forget back in the Other Networks list….!