If there is no gps available, does the Mini 2 rely on internal sensors to obey instructions from the remote?

If the indoor space is large, is it relatively safe to fly?

Is there any printed or video info on this subject?

many thanks,

You can fly normally, even in a dark room (without VPS = ATTI mode). However, I would then mount the propguards. In a normally lit room you can also fly "unsecured".  Video enough on youtube...keywords "mavic mini indoor flying"

The Mini 2 uses Occusync 2.0 which is based on 2.4GHz & 5.8GHz WiFi protocol for communication between the RC and the drone.  GPS is used for visual navigation in the DJI Fly and for RTH.  

Hello there buehlerbg. Thank you for reaching out and for sharing these information with us. Please be careful while flying indoors as the DJI Mini 2 stabilization feature may experience interference and might affect the said drone. In addition, if you really need to fly indoors kindly please use a DJI Mini 2 Propeller Guard and activate the Payload mode on the DJI Fly application. The DJI Mavic Mini Propeller Guard protects the propellers and other objects from damage. Just a reminder that the DJI Mini 2's Vision System cannot work properly  in any of the following situations posted below. Kindly please fly your drone cautiously. Please be safe always and have a safe flight always.

I had no issues flying indoor.

No issues for me flying indoors with no gps at all. Just have to be careful on the sticks. Boring video just an example.