If you are having difficulty connecting your iPad (4th generation or earlier) to your iPhone hotspot iOS 15, try setting your personal hotspot setting to "maximize compatibility".
iPad Pro 9.7-inch WiFi
Correct.
On iPhone:
Settings > Personal Hotspot > Maximise Compatibility - set to ON
This setting is to allow older Apple devices, and other manufacturers devices, to connect with modern iPhones. When set to OFF, the iPhone hotspot is forced to use 2.4GHz WiFi in preference to 5GHz.
iPads on iOS 10.3.4 no longer connect to iPhone hotspot iOS 15
