I see folder with question mark flashing

You can try other startup options as well....I would suggest trying the macOS recovery over Internet you can find the combination you can use at Mac startup key combinations - Apple Support

What happens when you try to go into recovery mode? That folder means that the OS has become corrupted and is not able to load. Either the files to the OS have become corrupted or the hard drive itself could be failing. What MacBook Pro are you using?

If you erased the hard drive (which it sounds like you did) and the install did not finish, then this is why you are seeing the folder with the question mark. If you aren't able to get it into recovery mode, you may want to get in touch with Apple Support and have them assist you with trying to get you where you need. If they are unable to do this, you will have to take it to an Apple Store or a certified service center to have them take a look and see what they can do. I don't know what to try as the Command + R always works for me unless it's an M1 model which wasn't available in 2015 where you just press and hold the power button.