There is no quarantine in most countries now, so Spain is no different.
I seriously question the generalized statement that "you are expected to continue working." Again, in most countries now, there are public health guidelines for how to manage Covid cases. They are much more nuanced than just "go to work but wear a mask". The guidance and the practices in Spain are very similar to most of our home countries/regions. As
@phildimashq points out...
The symptoms, Covid test results, and timing are all considerations. Both self-isolation and masking are important tools for managing Covid, which is all around us.