I use the latest 5.26 (2020/05/18 00:22) beta version and I can hear both Naomi & Dreamcast emulators running fine... I tried changing resolution and removing bezels, but i still get black screen. 5.25 was fine with both...
What are your hardware specs and what kind of monitor/tv is connected and how? (HDMI?)
Did you try Reicast for dreamcast?
I am on an i3 3470 (Intel GPU) and have it connected through VGA...
I did try Reicast. I worked, but was waaaaay to fast and had no sound.
to fix libretro core for dreamcast, try to delete retroarchcustom.cfg (make a backup first).
for standalone (reicast), delete the reicast folder in the config.
It all magically got fixed with the updated 5.26 2020/05/27 01:52 version! Yay!