dutch is a bit harder to understand. like some german dialects that not every german understands either, like swiss german, luxemburgian or friesian (also spoken in the northern parts of the netherlands), or plattdeutsch.

i grew up in austria and in the north of germany so i got an early appreciation for understanding dialects. yet learning dutch took me a few months of staying in the netherlands. on the other hand when i visited luxemburg people were shocked that i could understand them when they spoke amongst each other

Frisian is not a dialect, and is not usually spoken outside of Frisia (the Dutch province). In German Ostfriesland they do speak a German dialect with Frisian roots.