Generally the planning consent for the building requires a certain number of car parking spaces for each lot.
I am going to say that going by plans I have seen for strata, the builder would have put in the minimum number of parking spaces for each lot.
You may not have a car and say that your garage is superfluous.
But given that you are changing the number of car parking spots for your lot, this conversion would probably require council approval.
You can just do the conversion on the quite but you risk the OC making you take it down until council approved it.
BTW it’s unlikely to get council approval because it would breach one of their planning conditions.
Be circumspect about what you are doing and see what happens.