[fauigerzigerk]

You are probably referring to the non-habitual residence scheme.

As far as I know, the 20% tax rate only applies to domestically sourced income. Income from Ireland would be exempt from taxation in Portugal if it is taxed in Ireland.

I'm not sure if and how this scheme affects your social security contributions and eligibility for health care and pensions.

If you don't speak Portuguese well enough to really dig into this yourself, I would suggest you get professional advice.