I deleted Macintosh HD and Macintosh HD - Data. Now there is an icon of "files not found". How to solve it?

The file with ? means the Operating system has been deleted. Therefore the computer can not load anything.

Solution, turn off computer, plug-in the charger to computer, power up AND Immediately hold down Command + R keys, This is recovery mode. It takes long to load. Once loaded make sure you are connected to Internet. Now, choose to Reinstall macOS in the options offered. Allow it to download the OS. It will install the OS.