Why?? That can't work with the terrain and current buildings in Lisbon, there simply isn't enough space for a car per person. And I can't imagine a livable city with so much space and money wasted for parking and roads. ( Due to induced demand )
Improving public transit is a much better option, especially considering Lisbon has some decent infrastructure already ( the tram and metro networks seemed pretty decent from my trip there just at the start of the pandemic).