Is 4L of engine oil enough for maintenance, or do I need to buy 5L?

Actually, 4 liters is definitely enough.

Actually, it's enough, it couldn't possibly be insufficient. 😄

4 liters really isn't enough; I buy 5 liters. The original manufacturer offers 5-liter engine oil, but I purchase from another brand. Also, the benefit of having a little leftover oil is that when I feel the oil isn't performing well, I can add the leftover, and it feels much better to drive.

There will be a little left with 4 liters, buying 5 liters would be purely a waste.