I have searched online a fair amount and also on here and have not found any info about one of the resolutions I have found for this problem.

Most of the discussion involves a bad seal at the flange allowing sewer gas in, and that is normally what is the problem. What I noticed while I was working on my toilet flange was that the smell appeared to come from the floor. The floor had absorbed the bad smell from a previous bad seal and caulked base.

Here is how I came about this. While I was working on replacing the flange, after removing the old flange I had to stop till the next day and I used a small nerf football and stuck it in the pipe, sealing it well. The room still smelt like there was sewer gas coming in. That got me to start wondering, but I figured it was residual gas and would go away.

Next day before I removed the football it still smelt like sewer. I got the idea that it was the floor where the old toilet was because it shouldn't have smelt like that while the pipe was blocked.

I proceeded to install the new flange and toilet with a sani seal and put water in the bowl. Smell persisted. I then caulked the base of the toilet to block any possible odor from under the toilet. The odor persisted. The new toilet base had a smaller footprint than the old toilet, so I tried various things to clean the smell from newly exposed floor. Eventually what I found to work was I let some orange goop sit on the floor for a while around the toilet and when I cleaned that off, the smell was mostly gone. Then I used a bit more orange goop and scrubbed on the floor well. The next day the smell was totally gone.

So, if you are having a smell from a new toilet install and are sure your seal is good on the flange, it might be your floor that smells and I would recommend cleaning it up good with orange goop and also letting the goop soak on the floor for a while. Best way to check for a smelly floor is to plug up your flange with a small nerf football and see if the room still smells after some time.