What happened when Mafia III was updated to Definitive Edition: the game received a big patch that was supposed to make some gameplay improvements. In PS4 and XBOX One S this patch had around 10GB. Its not listed in patch notes, but they definitely made some changes in graphics, In Xbox One S and PS4 the game looks sharper, and things like dust when driving on a dirt road are improved. So, the game didn't just receive new DLCs and a new logo.
The problem is: for both PS4 and XBOX there is a single patch for entry and pro consoles, and this patch removed the improvements that were released years ago specifically for XBOX ONE X and PS4 Pro. So, the version of Mafia III right now for XBOX One S and PS4 are the same ones for their pro brothers, so the 4K is gone as well as the graphical improvements in texture, reflections and other stuff. Both PS4 pro and XBOX One X received in November 2017 a patch that introduced HDR and Full 4K resolution:
https://news.xbox.com/en-us/2017/11/16/inside-xbox-one-x-enhanced-mafia-iii/
The difference between the enhanced version and the regular one is huge, specially in XBOX One X. For example, cars textures in PS4 and Xbox One S version are really weird because at some moments the car reflection is blurry and low resolution. So, right now all those changes are gone, because for some stupid reason people released a single patch for entry level and pro consoles.
So, all you PS4 Pro and XBOX One X asking about "what happened to Mafia III?", this is what happened: you are now playing the same version of the game PS4 and XBX S players have. Yes, in those consoles the cars have poor and weird reflections and textures.
I'm afraid people who were behind Mafia III DE didn't even knew there was a specific version for XBOX One X and PS4 Pro.
Its a problem thats easy to fix: they just have to go back to previous patch. Its no difficult to release the previous patch with the updated logo and opening screen and with those adds that try to convince us to buy the Trilogy bundle.
So, my advise is: when you get in contact with 2K support, try to be very specific and mention the last patch removed the enhancements for pro consoles, and when we buy the game, both PSN Store and Microsoft Store told us the game is optimized for the pro consoles, and right now as we speak IT BECAME A BIG LIE. Mafia III DE currently has only on version in both consoles. THEY MUST PATCH IT AND FIX THIS UNBELIEVABLE ISSUE. Its not acceptable that they released a DE that completely removed the enhancements for pro consoles. People who previously owned this game in pro consoles are now stuck with an inferior product: its that what a Definitive Edition is supposed to be?
The thing is: can we expect better from a company that released WWE 2k20 in the state it was released?