Method 1

hugo new posts/<name-of-post-file.md>

Method 2

Directly create a MD file under content/posts and add frontmatter manually / copy from a existing md file.

Method 3

Learnt from a hugo theme(PaperMod) documentation here

Create new post md file based on a archetype.

Before doing this, add the archetype md file at archetypes/post.md

hugo new --kind post <name>     # name must have .md

or

hugo new -k post <name>       # use -k instead of --kind

But above creates new md file directly in content whereas I want it in content/posts/ (I could not see md files appear as posts in this theme until the md files are in content/posts/). Its not a problem because I can easily change this by:

hugo new -k post posts/test4.md

Also check bash script to create post in Hugo based on this archetype approach.

and now new md files are added in content/posts/ and will be based on the archetype you set.

Also check: Automatically set current datetime in new post.