In NSW, functions of the chair are set out in section 42 of the SSMA. They don’t include over-riding the secretary whose functions including giving notice of each meeting specifying the business etc etc.
If you use your right as an owner to request a meeting to consider the retaining wall, the secretary can either do so or not, in which case you go to NCAT. See section 106 about duty of the OC to maintain common property and section 126 about relevant orders.
Your OC may need a new secretary soon. Decide now whether you’re interested in the job.