Yoast 9.4 currently states at SEO -> Tools -> File editor:

File editor
This tool allows you to quickly change important files for your SEO, like your robots.txt and, if you have one, your .htaccess file.

The current wording implies that you just need the .htaccess file to be available, regardless of webserver software. However, the check to show the editor primarily checks for server software, not the availability of the file. So even if you have a .htaccess file on nginx (which generally does nothing) you won't be able to edit it.

I suggest changing the wording to clarify the checks a bit better.