Setting up a Wi-Fi hotspot on iOS13
There may be a couple of reasons for it. 

First option, try applying these tweaks:


Disable or turn off Personal Hotspot.
Sign out from iCloud.
Restart your other device.
Sign in to iCloud again.
Then re-enable Personal Hotspot.


After refreshing and enabling Personal Hotspot on both your iPhone  and other device, retry connecting through Wi-Fi.

Second option, toggle Airplane Mode on and off.

This is another simple old trick you can try to get rid of minor errors affecting the phone’s wireless radios including Cellular Data and Personal Hotspot. It works by giving a quick restart to the Wi-Fi features on the phone. Here’s how it’s done:


Tap Settings from the Home screen.
Select Airplane Mode.
Toggle the Airplane Mode switch to turn the feature ON. This will disable wireless radios on the phone.
While Airplane mode is enabled, turn your iPhone off and then back on again.
After it boots up, go back to Settings-> Airplane Mode menu.
Then toggle the switch to disable Airplane Mode again. Wireless radios on the phone are then re-enabled.


After performing the Airplane mode, go to your iPhone Settings->Mobile Data menu, then make sure that Mobile Data is enabled. If necessary, toggle the switch to enable the feature.

Third option, Reset network settings on your iPhone

This will erase your Wi-Fi networks and other network-related settings and server settings on the phone. Network errors and Internet problems that are tied to incorrect network configurations are likewise cleared out in the process. Here’s how it’s done:


From the Home screen, tap on Settings.
Tap General.
Scroll down to and tap Reset.
Select the option to Reset network settings.
If prompted, enter your device passcode.
Then tap the option to confirm network settings reset.


Your iPhone will reboot automatically when the reset is finished. As soon as it boots up, set up and reconnect to your Wi-Fi network or enable Mobile Data and Personal Hotspot to retry using and sharing your Internet connection with your other devices