Understand the difference between cultural appropriation and Cultural Mis-Appropriation
Cultural appropriation is ok^ (as long as you are generally respectful)
Cultural Mis-Appropriation is when you take something and use it without the care or honor that it deserves. That is not ok.
As with almost everything that involves humans, this is a spectrum and doesn't fit into neat little boxes. Also the will always be someone who is offend. And someone who is offended that they can't get away with something, even if it is horrible mis-representation.
A western person wearing a kimono, is ok. Because historicaly it was just everyday clothes. (Think how offensive it is to see a Japanese person wearing trousers or a suit jacket. It is not!) It is just normal cultural exchange of ideas. In fact it is seen as a good thing, because it is keeping a part of Japanese culture alive.
Like wise using flax (grass) skirts as part of a fashion line, is ok because they were just everyday clothing.
However if someone was to have a fashion line (outside of NZ^^) with a Korowai (see link below) that would be Mis-Appropriation. This is because a Korowai is Taonga, a cultural treasure. Something which is given to respected elders. It would be seen a cheap and tacky, to have as a fashion item anyone could just buy off the rack.
Jacinda Ardern, New Zealand Prime Minister, wears Korowai to meet Queen Elizabeth
Understanding if is something is, Taonga / Sacred / Precious, is important to understand where you place that idea is going to be ok. Take something precious and put it somewhere tacky. Yeah not cool.
Cultural Mis-Representation may be a bigger issue
I think something you need to be careful of is Cultural mis-representation. If you have one group who are portrayed as been 'dirty dumb savages' and portray them as lightly disguised 'Kangroo Islanders', that is not cool.
One or the other, may be ok; but by joining them together you are inadvertently saying present day Kangroo Islanders (or those like them) are dirty and dumb. Which is not cool.
Although that may be Ok, if you have a story arc where the protagonist thinks they are dumb, but then learns they are different with different values, and are culturally rich and highly intelligent in their way. i.e., make it about personal growth and understanding of the protagonist who was 'dumb' to underestimate the 'savages'.
^ As a side note if you were to say any Cultural Appropriation is bad, well you are walking very close to Cultural Segregation. Which is also a bad thing.
^^Inside NZ they should know the importance of a Korowai and when it is ok to wear one