How the comma works when I list things on a sentence?

Every time I write something like:

"She is interested in surfing, snowboarding and skateboarding"

The grammar checker suggests me to fix and add a comma before the end, becoming:

"She is interested in surfing, snowboarding, and skateboarding"

And the grammar checker explains:

The serial comma (also called the Oxford comma) is the last comma
before coordinating conjunction and the final item in a series. Its
use is considered a matter of style and is cause for much debate. Many
style guides require the serial comma, and a few advise against it.

There are times when it must be used to avoid confusion or ambiguity.
For the sake of consistency, we recommend always using the serial
comma. However, consult your style guide if you are uncertain.

Depending on the context, a missing serial comma may cause ambiguity.
Are the brothers named Adam and Jane?

Ambiguous: We have received RSVPs from my brothers, Adam and Jane.

Clear: We have received RSVPs from my brothers, Adam, and Jane.

Incorrect: Make sure to pack towels, sandals, sunscreen etc.

Correct: Make sure to pack towels, sandals, sunscreen, etc.

I feel this strange, in Portuguese we never use comma in this situation to remove the ambiguity, moreover, it is wrong to use it. Should I use in English?