A lot of people move to Portugal planning to work once they arrive. For example, they may come on a D7 visa and then hope to find a job locally. The issue is that there can be a long gap between arriving in Portugal and getting your AIMA appointment and residence permit.
If you want a standard employment contract in Portugal, I would say you need legal residency, as that is one of the requirements. However, as a non-resident, you can still own a company in Portugal, so there may be other ways to work that do not involve a formal employment contract.
— Sandra Gomes Pinto
So no, you generally cannot arrive in Portugal on a visa like the D7 and immediately start a normal local job while waiting for your residence permit. There may be other ways to work, such as owning or operating a business, but that is different from taking up standard employment.
If your main goal is to start working in Portugal as soon as possible, a visa route designed around employment may make more sense. The D3, for example, is supposed to have faster processing times.
Thinking about Moving to Portugal?