Hotspot automatically turns off/90s auto hotspot disconnect

Hey there, I am facing an issue I have two iPhone first one Is iPhone 7 and second one is iPhone 12 Pro Max. I want to share hotspot from iPhone 7 to iPhone 12 Pro Max but when I turn off the screen Wi-Fi from iPhone 7. Hotspot automatically disconnect on 12 pro max. The problem is that sim jack of 12 pro max is faulty so I share hotspot to 12 pro max from iPhone 7 and using same Apple ID I receive incoming calls on 12 pro max.. but due to continuously auto disconnecting issue of hotspot causing problem I cannot receive calls on 12 pro max because it needs an active internet connection like same wifi or same hotspot connection.

unlike android hotspot when a device is connected and even screens are off but in background hotspot will work and not disconnect when the user himself not disconnect or turns off the hotspot.

min simple words I want to turns off the 90s auto hotspot disconnect feature

need urgent help, Thank you