In the meantime I just use DVDstyler to author the discs. That level of education and suggestion is all I can do. Ive warned them for years that dvd authoring is becoming more and more untenable, and that they should consider upgrading to a file-based playback system.
Like you, it’s becoming increasingly difficult to deal with this on the Mac, but that’s more the client’s problem, and not mine. I still have a “legacy” client from 25 years ago who has been modifying the same tour-bus videos I originally edited for them in the 90s, and I always have to make a DVD for them, because that’s the only format the on-bus playback systems supports. I can’t fathom why Resolve would need to support it in any significant way. There are authoring tools (albeit rapidly shrinking in availability) that already exist to author bluray material. Supporting optical disc authoring capabilities is not where modern production tools should be spending any amounts of time and resources to develop.