The only thing you can do in this isntance is add a little noise to the image. This stops the stepped-gradient effect happening when you start adjusting things. The noise can then mostly be removed afterwards.
It isn’t perfect, but can stop colour banding from occuring when manipulating 8 bit files.
Building on this idea: check out f3kdb: https://f3kdb.readthedocs.io/en/latest/