If you have an Intel Mac, then try booting into Internet Recovery Mode using Command + Option + R.
If you have an Intel Mac, then also try a PRAM Reset (hold the PRAM Reset for two chimes).
Please always provide the exact model of your Mac when asking for assistance since different models may have different support strategies. You can get the exact model of your Mac by entering your system serial number here:
Check Your Service and Support Coverage - Apple Support
If you have access to another qualifying Mac, then you can create a bootable macOS USB installer using the instructions in this Apple article:
How to create a bootable installer for macOS - Apple Support
A qualifying Mac is one which can run the installer you are downloading, but the Mac does not currently need to be running that OS. Here is an article showing which versions of macOS are compatible with various Apple hardware:
https://eshop.macsales.com/guides/Mac_OS_X_Compatibility
For downloading macOS 12.x Monterey, you can use most Macs from 2015+, but check the list above to confirm.
However, if you have a 2018+ Mac, then a bootable USB installer won't work unless you previously adjusted the security settings to allow booting from USB since this setting can only be adjusted while booted into Recovery Mode which you cannot do at the moment.