Been running 18.4 on a number of devices and they are all fine. The only device that has support for AI is my M1 iPad Pro, but haven't really messed around with AI. I thought 18.4 would affect the battery as AI had been enabled (in europe) but its as good as it always has.
Other devices I have been testing with 18.4 are, iPhone SE 2 & 3, iPhone 11, 13, 13 pro, 14 and a few 16 devices.
iPads are the iPad 9, Air 3 and M1.
My 13 pro has started to show a bit of battery degradation recently, but I suspects that's more to do with me having enabled smart devices with Apple Home.
I did have an odd BT issue recently in my car after an update, think it was 18.3.2, but that seem to have disappeared after updating to 18.4.
Oh, lately I have had a few users complaining about Apple relay in a company WiFi environment (802.1x), not sure its iOS related but have had a few complaining that its keeps switching on and off. Its only been on networks with .1x tho.