iMac does not boot

Any help is appreciated to get my iMac up and running.

I have a fusion iMac from 2015. It has a 128 SSD and a 3 TB Hard drive. I am unable to boot it up because I get a circle with a line through it and it says support.apple.com/mac/startup. I went into Recovery mode and I can't reinstall MacOS because there is no disk drive available.

I looked at Disk Utility in the Recovery mode and see the following drives available:

• Apple SSD SMO128 G 123 GB PC Internal Physical Disk
• ST3000DM001 Media - 4.14 gb uninitialized

Disk Images:

Apple Disk Image (can partition) - 2.15 gb

OS X Base System (no erase, partition) - 2.01 GB

I tried to mount the ST3000M001 but it did not mount.

What should I do to reformat the drive so I can reinstall macOS Big Sur?