Short answer
The D8 digital nomad visa is for remote workers employed by a foreign company or self-employed with foreign clients. You must show a stable income of at least four times the Portuguese minimum wage per month, plus 50% for a spouse and 30% per dependent child. You also need proof of remote work, accommodation, and health insurance. Rules can change, so confirm current thresholds with the Portuguese consulate or immigration service (AIMA).
General information, not legal or tax advice. Rules and amounts change: confirm with official sources.