Do you know of, or recommend a FITS to DNG converter?

If you use Python. I just released a FITs to DNG convertor on github. It has extensive support for DNG - including arbitrary metadata, tiling, and JPEG/JXL image compression.

https://github.com/mu-files/mu-rasppi/blob/main/docs/README_astro.md 

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ImageMagick is a robust open-source package that can read FITS and write over 99 other file formats, including DNG. I've never tried that particular conversion path, but ImageMagick is easy to install and try.

This NASA page lists several apps that claim to convert FITS to TIFF.  You could then use Adobe DNG Converter to batch convert the TIFFs to DNG.