If I use nVidia Control Panel and disallow apps from using their own brightness settings and adjust the video instead using the nVidia Control Panel sliders, I can get blacks to be black and reasonably good color and gamma on the video in PowerDVD. But those settings, of course, are wrong for all the other video apps I use (most often, the Windows Movie & TV app).
The Windows 10 upgrade to 1903 took place for me on 7/27/2019. But the earliest System Restore point I have available is 8/5/2019. I tried it, but the problem was still there and I undid that System Restore.
The nVidia driver is 23.21.13.9125 dated 3/16/18, and I assume it's been there since roughly then.
Any ideas on what may be causing this sudden recent change to excessive playback brightness?