There is a particular kind of stuck where you sit down to pray and nothing comes. Not doubt exactly. Just no words for whatever this is.
Paul addresses it directly. We do not know what we ought to pray for. He does not present that as a failure state or a sign of shallow faith. He presents it as the ordinary human condition, and then says the Spirit helps us in it.
Notice the preposition again. In our weakness, not instead of it. The wordlessness is not removed. Something works within it.
This is quietly enormous if you have ever felt disqualified from prayer by not knowing how to start. The gap you cannot bridge is being bridged from the other side, in groans too deep for language, while you sit there with nothing.
You do not have to arrive articulate. Sit down anyway and let the silence be the prayer.