VM folder suddenly appears in HD

A folder or a volume? Where exactly are you seeing this?

VM usually means Virtual Memory. As part of converting to APFS a VM volume is created.

You should NEVER delete anything that you don’t know about.

I noticed this after a fresh install of High Sierra so I asked support. They told me it was normal and part of how APFS works. Here's what they said:

"All Unix based style systems use visual memory (vm) for normal operation and swapfile0 is a part of that; when the computer need more memory it can swap idle portions of memory contents to disk."

I'm wondering why they chose not to hide the folder, I thought it was a bug.

I don't why this appeared. I don't see it in any of my macs.

I suggest you try restarting in Safe Mode, then restart normally again. Does it remain?

Does the modified date change?

Wonder if anyone is ever going to respond to this. BTW, it looks like that should actually be 10.13.4, shouldn't it?

Did appear yesterday on my MBA. Contains a swapfile.

see also https://discussions.apple.com/thread/8116876