Hi, new dronie, how do I turn of GPS on my spark please?. marek

As far as I know, you cannot.

No ability to manually switch between GPS and ATTI mode

By losing GPS signal and with it the home point too - you really don't want that to happen...

thank you all clear

I learned to fly ATTI with the P4 and when i was in problems i would just switch to GPS mode and repeat until i mastered it. Spark can be used the same way, using the "DJI Assistant 2 development module" and set the sports mode value to 3, so that sports mode will automatically default to ATTI, i am not going to tell you how to do that, do your own research, seek and you shall find.

Hi marek, in fact, you can not shut down the GPS function manually, the drone will determine itself, when you are in a place without GPS signal, the drone will switch to passive ATTI mode accordingly.
But please kindly note that the drone might be limited when there is no GPS signal, please refer to the picture below:

Above chart  at the top, it says when the gps signal is weak,the  status indicator is flashing yellow.
But on the right hand column underneath, it says indication "none". Could you clarify please?.