Erased disk utility now can’t download OS

Boot your Mac in recovery mode by holding the Option-Command-R keys while starting up.

How to start up from macOS Recovery - Apple Support

Then follow guidance here:

How to reinstall macOS - Apple Support

• If you use Option-Command-R to start up from Internet Recovery, you might get the latest macOS that's compatible with your computer. That'd be Catalina for yours.

The others have you covered for the next steps. Just make sure to erase the internal SSD once more.

The point where you initially went wrong was just after you erased the internal SSD. Instead of rebooting the computer....you should have just quit the Disk Utility app and selected the "Reinstall macOS" option.

Since you rebooted the Mac after erasing the internal SSD, the system ended up booting into an older version of macOS installer than you had accessed previously. This is why Disk Utility is only showing "disk0s2" instead of a volume name since older versions of macOS do not understand the new drive layout & APFS file system used by macOS 10.13+. To install an older version of macOS 10.9 Mavericks, you will need to erase the internal SSD again so the internal SSD contains the MacOS Extended (Journaled) file system required by older versions of macOS (make sure to retain the GUID partition type).

There are two disks shown.

the first is Apple SSD SM..., of size about 250 GB, which is the boot disk

The second, which you were looking closely at, is the about 2GB disk image, Uncompressed and Mounted from the Mac's ROM, that contains MacOS Base System, the stripped-down version of MacOS that runs Recovery and related Utilities, including Installer. It can not be installed onto, it is already full.