Unable to connect to mobile hotspot

Then it is suggested again from the handy link provided by @ Zurarczurx

Incase it was missed the first time, which can happen If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi + Cellular)

" If you can't connect to Personal Hotspot with Wi-Fi

On the device that provides Personal Hotspot, go to Settings > Personal Hotspot, then:

1. Make sure Allow Others to Join is on. 
2. Remember the device's Wi-Fi network name and password that appear on this screen. If you want to change the Wi-Fi network name, find out how to change your device name.
3. If you’re using an iPhone 12 model or later, iPad Pro 11-inch (3rd generation or later), iPad Pro 12.9-inch (5th generation or later) or iPad mini (6th generation), turn on Maximise Compatibility.* Then try connecting your devices to your Personal Hotspot again.
4. Stay on this screen until you connect your other device to the Wi-Fi network. 

On the device that needs to connect to Personal Hotspot:

1. Turn Wi-Fi off and back on.
2. Make sure that you connect to the correct Wi-Fi network. The network name is the same as the iOS device that provides Personal Hotspot and the Personal Hotspot icon might appear next to it.
3. If you see a password error when you try to join Personal Hotspot, check the Wi-Fi password: on the device that provides the Personal Hotspot, go to Settings > Personal Hotspot to see the Wi-Fi password.

* When you turn on Maximise Compatibility, Internet performance and Wi-Fi security might be reduced for devices connected to the hotspot.

➡️. Then there is the Issue of " Weak Security " over Wifi ⬅️

Recommended settings for Wi-Fi routers and access points - Apple Support

If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi + Cellular) – Apple Support (UK)

Note that some mobile plans don't allow hotspots.

Does the iPhone register in the Wifi umbrella of the computer ?

Mine does

Notation - My iPhone is Not Connected to the computer via a Cable