There seems to be a tonne of sensationalist reporting and clickbait around this already. What’s actually happening is that the Max Capacity and Peak Performance Capacity values will not be filled in for non-Apple batteries. How are Apple supposed to know the chemical characteristics of 3rd party batteries? Some of them are probably lacking the firmware values to support the calculation anyway.

Finally - the ‘Service Message’ says nothing about the battery needing servicing. It says as follows - emphasis mine:

“This iPhone is unable to determine battery health. An Apple Authorised Service Provider can service service the battery.”

.. if you want them to, and replace it with a genuine one. Your phone will work fine in the meantime.