"yet" in this sentence means "but". It is "detailed" which means there is a lot of information. "BUT/yet" still easy to navigate.

Not quite. In this instance, the author is contrasting 'detailed' and 'easy to navigate'. You wouldn't expect a high level of detail to go with easy navigation, hence the use of 'yet'.

No. "Yet" means "but still". Note that "still" in English can be used with the meaning "but still". Thus your sentence could also be written as two sentences without losing any of its meaning: "Amazon has an incredibly detailed help center. Still (or 'yet'), it is easy-to-navigate " I don't speak Spanish but my guess is that you cannot do this with "todavía". It would lose the meaning of "but". Is my guess correct?