Hi guys, I recently encountered this problem and i know it is a bug and I don't know if this was already solved before.
The invert color is missing there and I've tried to reboot the phone multiple times
My problem is it keeps happening to my device already 3 times.
But recently I found the solution. In the accessibility there is a color inversion toggler and if you switch it on an off the button in the notification bar will be back into place
I hope the devs fix this issue, I don't usually use that feature but it disturbs me. Also this phone takes forever to reboot