support.apple.com/mac/startup/2100f

It means the internal boot drive is not booting so the Mac is attempting to boot into Internet Recovery Mode, or you intentionally are attempting to boot into Internet Recovery Mode. The large negative error codes indicate some sort of network issue which could be with your local home network, or your ISP, or an Internet issue, or possibly even a hardware issue with your Mac.

You can try connecting the Mac directly to your router using an Ethernet cable and if necessary any appropriate adapters for a faster more reliable connection which bypasses any hard to troubleshoot WiFi issues. You can also try to power cycle the router and possibly even the modem, making sure to wait at least five minutes for them to finish booting.

If you have access to another Qualifying Mac, then you can create a bootable macOS USB installer using the instructions in the following Apple article. However, if you have a 2018+ Mac, then you won't be able to use a bootable USB installer unless you had previously modified the Mac's security settings to allow booting from a USB drive since this can only be performed by using the Startup Security Utility while booted into Recovery Mode/Internet Recovery Mode.

How to create a bootable installer for macOS - Apple Support

If you do have a 2018+ Mac and are unable to boot into Internet Recovery Mode or from a macOS USB installer, then you can "Restore" the Mac's firmware which will erase the drive and push a clean OS onto the internal drive destroying all data previously stored on the drive. This procedure does require access to another Mac running macOS 10.15+.

Revive or restore an Intel-based Mac using Apple Configurator - Apple Support

Revive or restore a Mac with Apple silicon using Apple Configurator - Apple Support

Here is an Apple article for various startup issues with steps on how to proceed. Without any details, I'm guessing you will want to look at the article for blinking folder with question mark screen.

If your Mac doesn't start up all the way - Apple Support

You can always have Apple or an Apple Authorized Service Provider assist you if none of the above suggestions allow you to boot into a macOS installer to attempt repairs.

You really should provide the exact model of the Mac and the version of macOS used so we can provide suggestions catered to your specific system. You can get the exact model of the Mac by entering the system serial number here:

Check Your Service and Support Coverage - Apple Support

Also, it really helps to have a bit more background details on what led up to this point such as whether the Mac just booted to this screen or whether you intentionally tried to access Internet Recovery Mode.

Writing an effective Apple Support Communities question - Apple Community