I am too facing this issue and it has been around since 2019 time frame. I've sent in my iPhone 11 in the past to the service centre thinking that it is a phone issue and to my surprise the service centre advised that they have received many of the same complaint and its no fault of the phone device itself.

There are certainly differences in the network quality especially when it comes to multiple SIMs tied to a single principle number. As an example, Maxis is unable to support VoLTE on those principle numbers that has multiple SIMs, and if you have multi-SIM they are unable to support the Apple Watch. I reckon all these are somewhat related.