SIP client that works

I am after a SIP client that works on current versions of iOS 16.

By work I mean an incoming SIP call actually makes a dark idle phone running today's iOS16 ring and the call can be answered.

This is not currently the case with Linphone or PortSIP which along with others clearly used to work. They register but do not receive calls unless the app is the active app. I used Linphone after CSIPSimple for years on Android.

I don't wish to sound ungrateful but I would rather not have lots of "Have you tried X" replies which I can already find by the dozen when I want "X works with this week's version of iOS 16."

Thank you.

Jon