Why does pressing CMND + R keys when turning on the Mac result in a "forbidden" icon?

Question

macOS

Tell me, this is the question: I installed Mojave on the old iMac (which officially supported the latest OS - High Sierra) using the utility, and accidentally pressed update when he asked, then he went into updates, and after that it turns on, but the white screen is all. I tried to restore OC via cmnd + r, when you press these keys, such a picture appears (I attach), after which it is extinguished.

I also tried restoring through the Internet, it seems to install something, after which the apple lights up and so it constantly burns

Answer 1

The Mac cannot boot from the installed OS.
https://support.apple.com/en-us/HT210901
You can try to make a copy of the data in the external disk mode, erase and check the disk, install the system.