I don't think tinkering with income tax brackets/credits is going to fix the actual problem - robust and steady job creation of good paying jobs.
There are ~11M people in Portugal, 3M of which are in Lisbon metro and 2M are in Porto metro areas. This leads them to having the same problem as Japan - the population is decreasing, BUT the countryside and 2nd/3rd tier cities are emptying out.
So housing affordability in the major cities remains poor. The youth therefore get squeezed out and emigrate, leaving an increasing tax burden problem paying for all the benefits given to the increasingly aging population.
My father visited his home town in the countryside in the last decade and found much of the town essentially abandoned. No one lived in the home he grew up in. His uncle owned an inn that had no guests, etc.
Meanwhile, Portugal remains a beautiful place and I will visit more in the future, and could even see wanting to retire there.