For example, if I want to collaborate on making a (non-computer related) textbook with someone, and we want to use git as a version control system. Should we use github/codeberg for this or is there a platform that’s more suitable for using git in nontechnical contexts?
Git is for text in general, not only for code. As long as it’s human readable (I don’t know if doc or odt files can be used), git can work with it.
diff wouldn’t be any useful but it’ll still work
Much easier to keep the content in plain text as markdown/LaTeX/whatever markup language and then use pandoc or pdflatex to convert it to docx/odt/pdf/HTML/whatever as needed.
There are ways to store office formats as single XML files, look up “flat XML ODF”. Those are more suitable for repos than ordinary zipped ODF or OOXML files.