If you've installed Sonic Mania using Heroic Launcher then you'll quickly realise that it launches in a windowed version that fills about 50% of the screen. Seemingly changing the in-game settings causes it to crash with a 'black screen of death'.
There's a fairly simple fix however.
You need to edit the
settings.ini file located in:
Set the following:
Save the file, relaunch the game. Sorted.