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I bought a new Aura SSD 480GB from IFixIt and after upgrading the OS to the latest version Big Sur I followed the instructions on this site to swap the drive. Once done and rebooted using command R and selecting Disk Utility it only sees 2.15GB drive and not the newly replaced one (480GB). Any help much appreciated. Not sure what to do.

you need to Install the big sur firmware for those SSDs, follow the steps below. and install the latest firmware for the SSD. https://eshop.macsales.com/Service/Knowl

You have installed the older macOS which doesn’t offer the needed NVMe driver. The systems firmware was updated to support the newer APFS file system when you first updated your original SSD to High Sierra or newer (Big Sur?) If you haven’t done that then you’ll need to put your original SSD back in and first upgrade to High Sierra or newer. When you did the Internet Recovery the older OS was installed not Big Sur. So you’ll need to go back into Internet Recovery, use Option and Command and R keys during startup, in most cases you’re offered the latest macOS that is compatible with your Mac which is Big Sur for this system.