Author of Material for MkDocs here. I totally understand that some people don't like Material Design, as it's just everywhere nowadays and can be considered a bit overused. However, with little effort, you can adjust the style of Material for MkDocs with a few lines of additional CSS [0] and fit it to your taste. For example, several days ago I did this [1] in 20min. Nevertheless, Furo is an awesome theme if you like to use Sphinx over MkDocs!

[0]: https://squidfunk.github.io/mkdocs-material/customization/#a...

[1]: https://twitter.com/squidfunk/status/1598341366869856257/pho...