Solved it, not a problem with ArrowOS but a Xiaomi firmware bug:I have just discovered a strange issue that I have heard of before but never experienced myself: I have two SIMs in my phone, both are "4G Calling" capable and I have activated that setting for both. With that setting I can see the caller ID on an incoming call on SIM2 but not on SIM1 ("Unknown"). If I disable "4G Calling" for SIM1 the caller ID is shown as usual.
[GUIDE] How To Fix The "Unknown" Caller ID Issue With "4G Calling" Enabled