Make Mac to treat my iPhone like a regular wifi router. I want it to constantly stay connected to my iPhone (XS) [duplicate]

After further experimentation I found that if I create a Bluetooth connection (pair) between iPhone/iPad it stays connected throughout screen locks etc.

Finally a working solution!

Turn off Auto-Lock on your iPhone/iPad. If you set Auto-Lock to "Never", the Personal Hotspot will stay active. Even with screen locked for hours.

No more disconnects after 1 to 5 minutes.

I had the same issue with 2 iPhones. It appeared that iOS 12 is saving power by disabling Hotspot broadcast then the signal disappears afterwards.

To fix this Go to iPhone setting -> 'Battery health' and disable the battery saving mode. You find a small link under 'Peak Performance Capability', the option once disabled disappears and cannot be enabled again.