Apress used Word templates back in 2013 when I did my first book with them. Manning let you use asciidoc or Word templates when I worked with them. I wrote my first book with them in markdown and translated to asciidoc using pandoc. There were so many formatting issues and I found the tools for asciidoc so immature that I ultimately went to using their Word templates on my next two books with them despite preferring purely text formats.
Now I'm working on my next book and I think I'm going to try self publishing. I'm liking leanpub's use of a markdown like format. But again none of this really matters. You can fix formatting later. You have to sit down and write!
PS Thorsten's "Writing an Interpreter in Go" is great: https://amzn.to/3yLTJjE