SSD not showing in Disk Utility or terminal

Does it show any devices in either diskutil which might be the SSD?

If a drive is formatted as APFS the listing is quite different to previous ones using HFS+ and so can be confusing.

If no drive is listed that could be interpreted as being the SSD then the next place to check is using Apple System Report. It might be listed under NVMExpress or SATA/SAS or USB.

If it is not merely a matter of confusion then the most likely cause is a hardware issue. This could be either that it is genuinely dead or I have seen on some occasions SSDs having been jarred loose from their socket and hence no longer connected to be seen as a boot drive. For the later taking the bottom cover off would be required.

See - https://www.ifixit.com/Guide/MacBook+Pro+15-Inch+Retina+Display+Mid+2015+SSD+Rep lacement/48251

OS X Base System is usually an Installer image. Size of 2.1GB may be just a pointer to Internet Recovery, from your Mac's ROM.

So you have no drives showing, and are not using High Sierra Recovery HD from a drive.

When a drive will not tell Disk Utility its Make&Model and a reasonable, non-zero capacity/size, it is either cabled incorrectly, lost power, or died.

Volume-view is useless for this task:

there are four drives in my Mac Pro, but all I can see is their Volumes.

Device View is much more like it:

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Ok, as you say it must be working hardware wise.

If you can boot to the Recovery mode then try this…

• Run Disk Utility (the GUI one)
• In the top left corner you should see a 'View' option and you want to select View all
• Then see if there is a top level entry called Apple SSD or similar - select this
• (This top level entry represents the entire physical drive rather than a partition/volume)
• If you erase this top level entry it will wipe all partitions and reformat the entire drive as a single new partition, for a Mac the standard options would be either APFS or Macintosh Extended (Journaled) with a GUID partition scheme

Warning - this will wipe your Linux partitions.

It sounds like your previous Linux/Windows efforts may have accidentally deleted the Mac partition and the above would be the easiest wipe to start again.

Once you have it as a 'standard' Mac format then you can use the Recovery mode to reinstall macOS.