Please see the list of solutions in the below TurboTax FAQ to help with resolving the activation code issue:

TurboTax 2019 and TurboTax 2020 requests license activation at every launch

If you continue to have issues please see the link below to contact one of our TurboTax representatives: 

What is the TurboTax phone number?

I have this same problem, except it is much more urgent for me, because my disk/code has been mislaid.  I have the box and the receipt but not the disk or code.

I am shocked that this very serious bug has apparently been around for a long time and TurboTax hasn't bothered to fix it.

We take your concern very seriously and wish to help address this.  Unfortunately, in this public forum, we do not have direct access to your account, so we invite you to please contact our TurboTax customer support team to assist your further.

I did eventually find the disk and code.

Perhaps TurboTax's demand for another activation was triggered by a change of internet gateway.  I originally activated TurboTax on my regular home internet (AT&T); but on Sunday, when I was doing my taxes, my home internet was not working and so my computer (the same one) was using my (AT&T) cell phone as a hotspot/gateway.