Can I apply ceramic coating outside without a garage?

It is possible but harder to get right. Outdoors, sunlight heats panels and shortens the leveling window, wind carries dust onto wet coating, and dew or rain can reach the car during the initial cure. If you have no garage, work in full shade early or late in the day, on cool, dry panels, with a dry forecast for the curing period stated by the manufacturer. A carport or temporary shelter reduces dust and moisture risk considerably.