On my Android 12 Samsung Galaxy S21 Ultra 5G configured as mobile hotspot I can find the Pi’s IP address under “Settings / Connections / Mobile Hotspot and Tethering / Mobile Hotspot / Connected devices” under a device named “krakensdr”, provided that the Pi is actually connected to my mobile hotspot.
To connect to the Pi using a browser (to access the KrakenSDR application) or using a Putty app (to access the Pi’s console) on my mobile simultaneously configured as hotspot I will have to enter the Pi’s IP address. Entering the Pi’s hostname “krakensdr” instead of the IP address will not work on my Android 12.
However if I connect from my Windows PC over WiFi to my mobile hotspot I can use “http://krakensdr:8080” to access the KrakenSDR application on the Pi or specify “krakensdr” as hostname to the Putty app and log into the Pi’s console. Typing “ifconfig” on the Pi’s console will reveal the Pi’s IP address under the tag “wlan0”.