After PHP7.4 didn't work, neither does PHP7.3

[shawnb61]

Did something change in RC2 to hide this? I've seen it in RC1 when I upgraded my MySQL and PHP before I was aware of the password encryption changes. It stopped the forum from loading altogether, and displayed the message very clearly to me.

Lots of changes since RC1... 

But the big generic "Connection Problems Sorry, SMF was unable to connect to the database" when there are authentication problems has been around since 2.0.  You see the exact same issues in 2.0.17 when the DB user specified in Settings.php meets the criteria specified above.