notepad ++ should support this.
It may try to go online to update iteself but it won't hassle you if the connection is dead and you can tell it to cut that out.
I tried various other markdown editors, such as MarkdownPad, but they all had some problems, especially when the document became larger, often becoming unbearably slow and laggy.
I already have Visual Studio (not Code) installed and really don't want to get Code just to edit markdown files.
I've been using Notepad++ for a while now as a text editor, but as mentioned it doesn't have a markdown preview feature. Something I really would like to have.
Notepad++ does show markdown commands in different colors, that is something, but it ain't the whole enchilada.
MS Store MarkPad does have a decent preview feature as well as being free.
The Notepad++ markdown viewer plugin is just what I was looking for. I'm already using Notepad++ as my editor for markdown files, so having an on-demand viewer is great.
I learned something else about Notepad++, there's an easy to install plugin menu.