“Gregory XIV's bull of excommunication as a penalty for such wagers was never specifically rescinded, but was abrogated along with all canon law provisions associated with the Ius Decretalium in 1918.”
While technically speaking it doesn’t take a bull to be a mortal sin, discretion and a well formed conscience matters here. There’s also a huge difference between $10 among friends, and $20,000 among cardinals or princes. The original prohibition was most likely to prevent the latter.
I'm not catholic but I don't think that's necessary in their framework, no. An action driving you further from god is a sin even if you can't articulate a material harm caused by it.
I suppose the logic is something like "creating and holding the kind of cynical distance from momentous world events that would allow you to gamble on them weakens your connection to god's creation and therefor god himself."
Also - the "Doge of Venice" ? What are the odds.