Odor from incision post tummy tuck. Is this normal?

At three weeks after the tummy tuck, the fact that there is still tape on the incision is most likely the cause of the odor.

I would guess that probably proper hygiene will correct the foul smell but this is still something that you should bring to the attention of your surgeon.

Generally speaking, a bad odor coming from your incision needs to be investigated. It is not normal.  It can be something as minor as fluid under your dressing that needs to be cleaned and changed.  It can also indicate an infection. I recommend you follow up with your surgeon immediately for an evaluation.