If you have a Tello drone - actually this is probably the case for any device that you need to connect to via wifi in order to configure/control from iOS / iPadOS - if you have issues with the app just not detecting the drone even if you're connected to the device's wifi connection, try the following:
1) In the Settings app, scroll down to the particular app settings and check that it has local lan access.
2) Forget your home wifi network so that iOS/iPadOS stops trying to connect to it when it doesn't detect internet access on the drone wifi.
3) Disable Mobile Data. Even if you're connected to the drone wifi and getting an IP address - if Mobile Data is connected, the software will not be able to connect to the drone.
Now it should work. Good luck.