A black screen after the battery drains completely is a common but stressful issue. Here is an Apple support's tip you can try: If your iPhone won't turn on or the screen is black - Apple Support. Besides, these steps may help you:
1. Force Restart: This is the most effective first step and won't affect your data. First, you should press and quickly release the Volume Up and Down button. Then, press and hold the Side button. Don't let go until you see the Apple logo appear on the screen.
2. Thorough Charging: You mentioned trying this, but the method is key. Please use an official Apple-certified wall adapter and cable, and leave the iPhone charging for at least one full hour. A deeply depleted battery can take a long time to show signs of life. Trying a different cable/adapter is also a good idea to rule out faulty accessories.
3. Connect to a Computer (Recovery Mode): If it's still a black screen, connect it to your Mac (using Finder) or PC (using iTunes). While connected, perform another force restart as described in step 1, but do not release the side button when the Apple logo appears. Keep holding it until you see the recovery mode screen (an image of a computer and a cable). Your computer should then offer two options: "Update" or "Restore". You should choose "Update" first, as it attempts to reinstall iOS without erasing your data.
If none of these steps work, it may be a more persistent software issue or a hardware problem that requires professional service. You can ask apple aupport for help.