How to stop iOS 13 Personal Hotspot dropping out after 3 minutes even when plugged into power?
The hotspot on iOS 13 is stable and solid for me to connect windows 10 and iOS and macOS from 10.13 and higher for more than an hour, so the presumption that iOS is the culprit might be worth investigating. 

At worst, your device needs an erase and install if its struggling to share out the network. Do you suspect your iOS device needs repair or are you in an enviromnemt where WiFi interference is high?