I used a Wordpress Plugin from the official WP downloader GUI. WP Export to Gatsby, but it’s not Gatsby-specific.
I chose it because it looked easy and had lots of ratings in the WP plugin “store” , as well as this blog post. haha
I used search-all-and-replace-all to mess with the front matter after exporting to markdown. I started from the same md file contents for each project.
I know there are command-line tools with more options, including this plugin itself: wp-gatsby-markdown-exporter/README.md at master · tinacms/wp-gatsby-markdown-exporter · GitHub
There are also scripts by other people that take the contents of a vanilla Wordpress content export and munge them into md files. I didn’t try any. I just went with a GUI option that looked easy!
(I’m code-ing out links because I can’t post more than one as a new member)