It all depends on the flying enviroment, there are no hard and fast rules***.
I am not being awkward for the sake of being awkward but the manual also tells you what should happen in the event of a disconnection.
I have not, as yet, flown the
Mini 2 out to disconnection at extreme range but I have had one or two disconnections in the 600m to 1km range due to the enviroment, trees, possible radio interference...that sort of thing, yet I have gone further than that elsewhere with out disconnection.
BUT, if every thing is setup correctly, homepoint, RTH height, failsafe settings etc. the drone has yet to fail to get home. So much so that I have also shut off the controller just to lieterally see what the drone does.
Watch out for wind, the
Mini 2 is better than the Mavic Mini but wind could still be a threat to it, especially if you set needlessly high RTH heights.
***HOWEVER, there is also the law that the drone is supposed to be flown such that you can always see it with your own eyes, and maybe determine its orientation, all without the aid of binoculars etc. My 'distant' flights have been over empty sea.