I love the setting of Brancalonia. I love the humor, I love the folklore, and I am currently learning Italian in evening classes to boot, so this is basically a perfect mix.
But I do not love that the authors picked D&D 5E as the rule system for this setting. Don't get me wrong, I find D&D 5E perfectly acceptable for heroic fantasy campaigns (and, in fact, I am running such a campaign right now). And I can understand this choice from a business perspective - it makes a lot of sense to tie your setting to the most popular RPG system out there.
However, Brancalonia PCs are not supposed to be great heroes, but fairly unimpressive never-do-wells. The rules deal with this by capping character level at 6, but I feel that this leaves the PCs with too little room to grow and removes much of the proper D&D experience. I'd rather use a rule system that was intended for weaker protagonists, rather than trying to distort D&D into something that is not.
So, what alternate system would you use for Brancalonia?
I'd recommend Pathfinder 2e's combat then, though I haven't played Brancalonia to know if it's a perfect fit.
Pathfinder 2E has a very similar power curve as D&D 5E. In fact, it might even be worse for Brancalonia as characters basically get their level as a flat bonus on everything.
PF2e has proficiency without level for a grittier experience, but even then I don't think it's the best option for low lives and ne'er-do-wells unless you limit it to about level 3. Might be worth looking at Hopefinder, which is a PF2e hack, but the default setting is a zombie apocalypse and I think it relies a lot on short stories.
If your bonis flat, talk to your doctor.
If bonis not flat for more than four hours, talk to your doctor.
There’s a rule variant called proficiency without level which removes the flat bonus.