We are talking about 3sqm here. If that is already too exhausting as lawn/paving... I think there is no solution other than to seek an exemption from the development plan and, as a last resort, disconnect from the property.
Why do you actually want to ride a bike into the garden?
Why does a wheelbarrow have to pass there – do you seriously want to wheel the wheelbarrow out of the garage door and then around the garage into the garden? That is overall not coherent and impractical.
You don’t want to spend €1500 on a sensible door, but at the same time you deny the lawn next to the garage because the [Robi] can’t reach it. For €1500, there are many [Robis] – which of course is absurd for 3sqm, but only makes the real dilemma clearer.