Test the idea. Light a cotton shoe lace until it's burning under it's
own steam, and then blow out the flame so that the cotton is smoldering,
releasing a steady stream of smoke as it burns. You now have a poor
man's smoke pencil. Hold the smoldering end of the shoe lace over your
floor flange (or what's left of it) and see if the smoke gets sucked
into the toilet waste pipe or blown out of it. If it gets blown out,
then it could be that the prevailing wind is pushing air down your vent
stack, and preventing sewer gas from coming up. If it gets sucked into
the toilet waste pipe, it's probably due to the wind blowing over your
roof.

I used a length of twine. (Shoelaces still packed somewhere in my moving
boxes.) Produced black smoke with the flame present, then white after I
blew the flame out. The smoke rose, but that's its natural tendency
anyway. It didn't rise fast when I held the string over the opening.

I then cut a thin strip, 1/4" by 3" of single-ply facial tissue and held
it over the opening. Wasn't sucked down or blown upward.

I dumped about a gallon of water down the drain. It simply went away. If
there is a blockage farther down the drain pipe, this test wouldn't
detect it. Maybe I should run a garden hose down the drain for five minutes.

R1