Not much more to add really.
Generally the
M2P will probably only fly in ATTI mode indoors, if it can't hook into sufficient numbers of satellites for OPTI mode flying. If you have "moded" your
M2P and can therefore select an ATTI mode to fly indoors, this may be the better option, as this should afford you a little more stability compared to letting DJI Go4 and AC communication process flick around trying to find the most suitable mode as you attempt to negotiate relatively narrow flight paths plus differing signal strengths with potentially errant signal reflections.
Unless you are really experienced flying in ATTI mode and flying indoors, probably not something I would recommend. Prop' noise is quite significant, as sound resonance reflects off multiple surfaces. Prop' wash in confined spaces I suspect might also play havoc with the AC's flight stability characteristics.
Good luck, if you really feel you want to give it a go.
Edit: It has been suggested in another post on this subject, the modification to Mavic's software to exchange one of the three pre-installed flight modes "Opti", "Sport" or "Tripod" can only be achieved by
hacking. I feel this suggestion would seem to be something of a misnomer. By definition hacking involves "
the gaining of unauthorized access to data in a system or computer." This is not the case with the Mavic series, where, as long as the correct version of DJI's Assistant 2 for Mavic is utilised it is perfectly possible to modify a very large number of the Mavic's flight parameters which broadly help to provide a stable flight platform so that anyone from Mavic series novice to DJI expert systems flyer can pick this particular aircraft up and fly it with an absolute minimum of training. Such a modification that would change any one of the Opti, Sport or Tripod flight modes to a switchable ATTI mode is a completely reversible process, and as such should not really be characterised as a "hack".