Charging iPhone 12 Max Pro

It is not only OK, it is a best practice to charge overnight. And you should never intentionally discharge the battery to zero; that will shorten its life. Charge when it reaches 20% or lower. This is primarily to prevent it from shutting down unexpectedly if you have to suddenly use it while the battery is low. There is a warning at 20% that you should heed.

The absolute best way to improve the life of your battery long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern. If you enable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates.

Christo295 wrote:

Thank you so much for the quick reply and explanations!! So it's OK to start charging it if at night, it's still has around 50% power?

Yes, you can charge it whenever convenient. Lithium Ion batteries can be charged from any level to any other level of charge, unlike older battery technologies. Here’s the long version tip on charging→When to charge your iPhone or iPad - Apple Community