I also have really worse network issues with my iPhone 12 I contacted the support and I did everything they told me! I know most of the solution they came up with won’t work, but I bravely did everything as well as the Diagnostik with Apple Support! Than I brought it to the workshop where they should fix my issue, so I went there and they told me my device is fine and everything works how it should be!
But the I feel like I bought a cheap trash device for a really high price! It’s disappointing and all my friends are happy with their iPhone 11 or Android devices gaming on 90 FPS