There are so many options but it genuinely depends on how your content is being generated. If you have everything in a giant CSV or JSON file then there's not much work to do at all. Many shops I worked with were used to WordPress and after WP released the API functionality it became possible to completely decouple the editing & publish function from the front end display. You can still use a securely locked-down WP install for content creation and editing, then just use the (also locked-down) WP API endpoint as your data source that gets fed into your site generator. Hugo has an awesome feature where if you feed it a URL it will go fetch your content for you, so it doesn't even need to exist in the /content dir prior to build. Thanks to the free tiers for Gitlab CI/CD or Github Actions, your repo only contains theme code and with a 10-line CI/CD config file and a container image that has Hugo installed, you just need a trigger to run the build pipeline - then you're left with the static site that you can publish anywhere you like.

If you don't need the user roles and editor experience you get from WP then you can feed your generator the content from any source you like as long as the files have the correct frontmatter to turn them into pages/posts. You might need a little glue script here and there to chain systems together, but it's not super difficult to adapt to whatever pipeline you need after you understand where your content comes from.