Indoors I am not surprised you get a no GPS warning but as has been mentioned there is a backup system (VPS?) that uses downward looking sensors to 'stabilise' the drone.
Providing there is sufficient light for it to work the latter is VERY good, cm perfect for me.
Perhaps, if you read the screen notifications carefully you may find this is available to you. (I forget precisely what I see, as per what follows.) A video recording screen capture app is VERY handy for 'capturing' these pop up messages.
When I fly my MM indoors I invarialbly get the warning of no GPS and then subsequent warnings about lighting and I have to confirm that I acknowledge (or something ) the warnings before my MM will fly.
That probably sounds vague but this, indoors, is now a routine procedure for me and, indoors, I no longer read the warnings providing they come in the correct sequence. Once the drone is in the air there is sufficient light underneath it for the VPS to work. (there is a single ceiling mounted light 'bulb' where I normally fly indoors so the drone very much sits in its own shadow)
With regards to moving out doors, it can take time for the drone to 'gather' sufficient satellites and for me, just outside my house, this could take minutes. I normally lift off before this and raise the drone to between 12 and 15ft so that it has a much less obstructed view of the sky. It normally gathers satellites much more quickly when up there. Note, this is a largely vertical climb. If it still doesn't gather sufficient satellites I will move it a few ft towards the centre of the garden.
This all uses the VPS to maintain 'stability'. If you have neither GPS nor VPS the drone reverts to ATTI and that is an entirely different ball game and should be avoided as it requires significant skill to use. (I do not have that skill.)
With regards to
iPhone app shows a dozen satellites overhead.
are you talking about the fly app or some other app on your phone?
