What jurisdiction would you choose to open a legal entity for a bootstrapping SaaS?

None. Just use Remote.com.

From what we were looking for, I liked Estonia and Portugal the most. But they have now tightened measures to open a business online.

I'm glad to hear that you're considering opening a legal entity for your bootstrapping SaaS! The jurisdiction you choose will depend on a number of factors, including the location of your business, the type of business you're running, and your personal preferences. Some jurisdictions are more business-friendly than others, so it's important to do your research before making a decision. I'm sure you'll be able to find the perfect jurisdiction for your needs!