There is a limited supply of apartments. If a digital nomad lives in one, then a native portuguese can't live there. This is basic math.
15 years ago Lisbon was in terrible shape, mostly collapsing due to rent controls.
And this is still the case to a degree. You have an enormous number of houses where the (older than, I think, 55) tenants pay 50 Euros per month that cannot be increased and the landlords pay more than that just in taxes and basic fees. So no renovation is done, everything is falling apart.
The rent comtrols have been there for the better part of a century, but they were only a problem when tourism boomed, rent control cannot be a cause of shortages if it was in place before without problems.