One AboutIslam.com article (I'm not sure if this is a fatwa) describes someone as having converted to Islam before saying the shahada. The article begins with a submitted question:
I am still a Christian who really wants to become a Muslim. Islam has become the only true religion for me ... I really want to live as the holy Quran tells me and I am even learning how to pray. But I have problems ... and I am afraid of doing the shahada ...
And the response contains:
Please know that even though you have not said the shahadah in an official way, you are already a Muslim because you have accepted the message of Islam. And this is between you and God.
About Islam Counselor, Can I Convert If My Parents Are Against It?, 2017
I'm not sure what to make of this. Logically, it makes sense: a genuine belief in the contents of the shahada is what's important, not verbalizing it. However, I have never seen this claim before, and it might be a "rogue" opinion.
Question: Can one convert to Islam without saying the shahada?