i bought iphone 13 one week ago. it drains 4 -5 percents overnight. is it normal?

If the phone is left on (not fully shut down) that is completely normal. The phone needs to use some power for things like keeping the time and downloading updates. If you’re worried about it I would recommend charging overnight.

Adding on to what Kurtosis12 said, no it is not at all bad to charge your iPhone overnight. iPhones have sensors that will tell it when it is fully charged and to stop charging. You can also turn on optimized battery charging in your battery settings. This will keep the phone at 80 percent battery most of the time it’s plugged in overnight, and finish the charge before you wake up.

The best thing that you can do for your battery is plug it into the charger overnight every night, so you will never have to worry about any kind of loss overnight.

Also make sure that Optimized Battery Charging is enabled on the phone. Settings > Battery > Battery Health

No, in fact Apple recommends it.