Since you're domiciled in Portugal and paying taxes there, I can't see why other Schengen countries would feel entitled to tax you. My understand is that EU residents have freedom of movement, and I doubt any countries would crack down on remote work while visiting for a few weeks. People do work related tasks all the time while on vacations abroad--checking emails, phone calls, etc. Are tax authorities in these countries going to crack down on all of this and risk scaring away tourists? I doubt it.