There is no connection possible with the app (neither on the iPad nor the iPhone) while the PI4 with HA has connection to the network.
Restart of the Raspberry also wasn’t successful.
Is the App not compatible with iOS 26.4 PB 3?
Working fine here. Do you try to connect internally from home network or externally?
Check you HA network settings in Settings > System > Network
Try to connect using homeassistant.local:8123 instead of your IP address.