Best outcome:-
Large dense well planned urban cities driven entirely by sustainable energy and smart AI intensive infrastructure. Population per city 5-10 million.
These cities surrounded by large climate controlled greenhouses where all food are grown from suitably bio-engineered plants to ensure very high yield at low resource utilization. City waster fully recycled to organic fertilizers as plant food.
High speed inter-city train services and planes facilitating travel between cities.
Population stabilized at about 8-10 billion.
Each of these mega-polis internally governed and autonomous. City conglomerations decide continental policies while planetary policies determined in a future version of UN. Nation states are obsolete.
Rest of landmass (about 40%) left to the wilderness to keep planetary ecology stable and recover from the destruction it faced in the 20th and 21st century.
When could this happen? Optimistically by middle of 22nd century.
Average human lifespan should touch 150 years by then.