In reply to Álvaro.

There’s no way you can build a website in a day with JAMstack without knowing some programming language and the way all this stuff glues together (services, APIs, …).

Yes, there is! Stackbit was mentioned in the article, but there is also
Sitesauce
Directus
TakeShape
Agility CMS
Netlify CMS
SiteLeaf
(not all equal solutions)