Welcome to the forum Foraes,
This does come up every once in a while.
That feature was removed a long time ago because it could happen that users who didn't understand it's working, might 'accidentily' use it, and leave it activated without understanding that it indeed alters the original sound quality, and then might later on put the blame on MusicBee for doing that.
I might have a suggestion for a compromise to bring this feature back without needing to resort to using a virtual device.
There could be an option to activate it for the instance when you want to do encoding with permanent loudness adjustment.
But it would then not be a sticky setting, but would only be active for that operation, and revert back immediatly after completion.
In that way you would have the option available, and it would avoid the risk of leaving it activated accidentily.
If this would be of interest to you, you could create a wish for it on the wishlist board.