I’ve been using Digikam for 20 years, and although it’s pretty good now, it has been a rough 20 years in some respects. Nevertheless I’d do it all again rather than suffer the trap of putting data into a system designed to prevent you getting it out.
Edits are essentially impossible to transfer between RAW development software, and even between major versions of the same software. It's not specific to Lightroom, Digikam, or Darktable. You would have to replicate everything, from the color science to quirks and bugs. Adobe literally ships previous versions of Lightroom's processing code in each new Lightroom version, to avoid messing anything up. As does Darktable (it still contains the previous code for compatibility) and any other software.
