iOS 15.1 has stuffed up my functionality on my Xs. Have spent hours with Apple support, had the phone checked with service agent, but still will not allow some devices to connect to its Hotspot. The touch function in some apps has become a farce. ??

Use these steps first

Restart the iPhone or iPad that provides Personal Hotspot and the other device that needs to connect to Personal Hotspot. Make sure that you have the latest version of iOS. On the iPhone or iPad that provides Personal Hotspot, go to Settings > General > Reset, then tap Reset Network Settings.

If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi

The Hotspot is a carrier-specific feature. Contact your carrier, if it is not appearing on your device.

Meanwhile...

Check the following

1. Network coverage and stability
2. Data Balance
3. On your windows (See if WiFi Auto Joins is enabled)
4. Also, check if you have any stronger WiFi signal around your computer.

Hotspot, VoiceMail (Visual or Normal) all are Carrier Specific features. Contact your Carrier (Cellular Service Provider), the agency that issued the SIM / eSIM to you.

No, this has nothing to do with the Carrier. After 15.1 ALL of mine AND my families iPhones Stopped connecting the hotspot.. this is 100% an Apple Issue. Not Carrier..