So, slap my hand here…
My issue was that in the WOPI setting, I carelessly set the my local IP with the wrong range (172.24.0.0/16 which is the range between my Docker containers) instead of whatever IP range my regular network devices were being assigned to by my AT&T router (172.71.0.0/0). Fixing WOIP to the latter made it work.
Now, heading over to make Talk work.
Cheers!