I've stumbled about the element on w3schools but as far as caniuse.com told me, the element isn't supported by IE, Opera Mini and the UC Browser for Android.
Would I be better by going with a <main> element or should I stick with a <div id="main">?
caniuse.com told me, the element isn't supported by IE, Opera Mini and the UC Browser for Android
That isn't what it says.
It says "Partial support" and:
Partial support refers to missing the default styling, as technically the elements are considered "unknown". This is easily taken care of by manually setting the default display value for each tag
So if main has the appropriate semantics, then use it. Just make sure to explicitly set display: block.
If the browser doesn't expose the semantics of using main then it will have no semantics, which is the same as a div.