@Qmit 

Deco M4 supports connection preference, X10 does not (yet). If you remove X10 from your Deco mesh, Connection Preference feature should appear in Deco app, when you add X10 to Deco mesh - that feature will disappear. All Deco units in Deco mesh must support that feature to have it available in Deco app.

In your case, if you plan to keep X10, try workarounds that might achieve same result, see: https://community.tp-link.com/en/home/forum/topic/227700?replyId=554140

  @David-TP Oddly enough after a few weeks now, my m4 has connection pref. but for some weird reason the x10 does not, i've checked multiple times, i'm guessing my m4 v2 updated pretty recently and is now allowing me to use connection pref. but my x10 still dosen't have the option for whatever reason.

  @Qmit After looking a lil deeper i've noticed that some devices have the option and some don't irrespective of whether they're connected or not, in the offline clients list 3 of my phones have the connecting pref. option while 2 others don't, one of my laptops have the option and the other dosen't, and my amazon devices + iot devices don't have the option at all, but i remember my amazon devices had that option before, i'm just really confused at this point.

  @Qmit it's litterally been an hour at most and the option has now disspaeared after re opening my app. At this point i don't know whats going on man