But what that implies is: Trinitarians should only pray in a way that non-Trinitarians find palatable.
That's not really an answer to the question of: is the Holy Spirit a creature?
I specifically did not answer your question as my intent was to present the natural conclusions of the two primary positions and let the reader make up their own mind.
To a Trinitarian, this should be a non issue. To the Trinitarian, God-Father, God-Son and God-Spirit are all the same so it should not make a difference as to which one to pray to.
It is only the non-Trinitarian that the question has any relevance and/or requires an answer. To that basis of theology, God is different from Son and from Spirit. In my experience, non-Trinitarians place more authority on God-Father and when Jesus tells them to pray to God, the interpretation is to pray to God-Father because Jesus did not tell Christians to pray in any other manner.
So in this issue of Theology, the first operative question to the believer is ... are you a Trinitarian or a non-Trinitarian. When that issue is settled in the believer’s mind, then the answer is provided above.