Hmm not sure of a solution then, mine is just there in the list (iOS 16.4.1a). I tiny think there’s a way to add an app if it simply doesn’t show up in the list of available widgets.
Another search result suggests a similar workaround.
How to make iOS 16 recognize app widgets
Change your iPhone’s language
Offload the app
Then reinstall the app
Change your iPhone language back
What this does is force the iPhone to re-examine the app and so discover that it does have widgets.
To change language on your iPhone:
Go to Settings, General
Scroll down and choose Language & Region
Tap Add Language…
You’ll be told that changing the language means the iPhone must restart, but it may not. If you already have a couple of languages involved, then you can drag to rearrange them and so set which is first.
Note, that the Naim app widget is an „old style“ widget. So it does not show in the „new“ list of widgets (via the + button).
Instead you need to go to the bottom of the widget screen and use „customize“.
The new widget type does not allow any interactive elements, I.e. they are suitable for this kind of widgets.
Yes; the new widgets can basically only display stuff. When you click them, they can bring you into the app itself, but cannot interact in the widget itself.
So you could have a “now playing” widget, but not including the controls the current one has.
(I read rumors Apple may further enhance the new widgets, now that they are more prominent on home screens and always-on displays with the Pro phones. Time will tell.)