what if when you push command-r at start up it doesnt do anything? The question mark just keeps flashing.

If your Mac starts up to a question mark

A folder with a flashing question mark means that your startup disk is no longer available or doesn't contain a working Mac operating system.

If the question mark appears only momentarily before your Mac starts up normally:

1. Reset NVRAM.
2. Make sure that your preferred startup disk is selected in Startup Disk preferences.

If the question mark persists, follow these steps:

1. Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off.
2. Turn on your Mac and immediately press and hold Command (⌘) and R to start up from macOS Recovery.
3. While in macOS Recovery, use Disk Utility to repair your startup disk.
4. If Disk Utility found no errors or repaired all errors, reinstall macOS.
5. If you still need help, please contact Apple Support.

I recall having to reinstall the OS on a neighbour's Mac when the machine wouldn't boot (flashing question mark). In that case, the only option available was to use internet Recovery. Note that it's best to use an ethernet connection if possible.

- Pie Lover

Other macOS installation options (from https://support.apple.com/en-us/HT204904)

When you install macOS from Recovery, you get the current version of the most recently installed macOS, with some exceptions:

• • On an Intel-based Mac, if you use Shift-Option-Command-R during startup, you're offered the macOS that came with your Mac, or the closest version still available. If you use Option-Command-R during startup, in most cases you're offered the latest macOS that is compatible with your Mac. Otherwise you're offered the macOS that came with your Mac, or the closest version still available.

See also Mac startup key combinations

Sorry I meant my post to be in reply to the original poster.

I have used internet Recovery a couple of times and it worked well. I may have even used it over a WiFi connection as the specific device didn't have an ethernet port.

- Pie Lover

Then, one of three things ;

1 - The computer is not an Intel computer and thusly

2 - the method suggested by previous posting by @ Barney-15E needs to be used.

3 - the computer needs to the evaluated by an Apple Authorized Service Centre.

Find answers and ask questions in Apple Support Communities

On the next page, you can Create a new post. It's helpful to include details like product specs, software version numbers, actions that cause the issue, and any troubleshooting you've already done.

Community etiquette guidelines

Is it an M1 Mac? Use macOS Recovery on a Mac with Apple silicon - Apple Support

That was a waste of time reading that. Not helpful in any way. I know this is a common problem there has to be a easy answer for this.

Not sure your reply was intended to me ( @ P. Phillips ) for someone else ?