I know (and have been using) the xlst json-to-xml() function for this
purpose, but it is a pretty basic result. I happened to try the JSON
to XML funtion in oXygen and got what I'd say is a much better result
where I had some unique elemeent names instead of everything being a
map or a string element.

I was poking around to try and find a tool/library I could use in my
conversion path and everything I'm finding is an online tool or has a
price. Currently I'm developing a conversion pipeline and can leverage
oXygen for this, but I need something I can build into a tool and load
into a Docker image for the production implementation.

Anyone have a suggestion?

BaseX is open-source and has more than the W3C functions, see
https://docs.basex.org/main/JSON_Functions for details.