Is it normal when car AC is on for long or long airway trip it will feel like it not cooling anymore?
After sometimes it will start cooling

No something is wrong with the cooling system.

The longer the AC remains running the cooler the car temperature should fall except there's an open window or door.

Even when the AC thermostat kicks in to switch off the AC, it restart so as to maintain the temperature you set it at.

Otherwise there's a possible leakage in the closed system.

When it stop cooling pack and open the engine bay. If the fan stop rotating for long it will not cooling. The thermostat sensor can sometime malfunction and it will cause overheating

Immatex:

No something is wrong with the cooling system.

The longer the AC remains running the cooler the car temperature should fall except there's an open window or door.

Even when the AC thermostat kicks in to switch off the AC, it restart so as to maintain the temperature you set it at.

Otherwise there's a possible leakage in the closed system.

I believe it’s this stuff I highlights
It will switch off and restart again

Nah, it isn't normal, something is wrong. When I leave d AC on for long in my car, my hand dey freeze sef, sometimes I'll have to turn it off or reduce it cause of the cold.