A fourth generation white man in america from english immigrants has no culture. I have no culture.
If a majority wears historical clothing from native groups it is appropriation.
If a minority group starts to wear t-shirts and jeans it's imperialism sometimes.
If there is no mix of culture or ideas it is xenophobia and segregation which is bad.
If there is too much mix or a mix in the wrong direction it is wholesale appropriation.
Historic and less privileged minority ethnic groups are disappearing and many languages and cultures will be lost and must be preserved. Not by white people but by textbooks.
If you go to India for summer vacation and come back with a henna mandala you have not equally exchanged culture. India has more people and but less power. It has more religions and a longer history of religion but is not an industrial super power on par with America.
You don't have to feel white guilt but you do have to listen to minorities about their culture. Someone from that culture approving an "item of appropriation" does not actually give you the moral right to wear it. However, someone from that culture disapproving of the "item of appropriation" removes any moral right you could have had to wear it.
Worship Japanese designers but only for their take on traditional american motifs. Wear visvim virgils but not fbts with leather fringe or bead work. Also don't wear tabi shoes- or do, whatever.
Buy from GAP, praise be, but do not consider the industrialization of the nation's that are manufacturing their clothes to be an act of imperialism- it's growing pains. Ethical assimilation.
Do not disturb wandering tribes in Western Africa and do not wear traditional patterns or silhouettes from them. However you may disturb them if they'd like to join the industrialized world and sell into misery and slave labor the next four generations of their people to manufacture your shitty GAP trou that will artfully pool for only five quid.
Support mega corporations and fast fashion as long as they are tasteful in their approach to selling you the style de jour.
Military haircuts, great. Military jackets, fine. Military badges, sometimes ok. Military medals, never fine. European military, same rules apply.
Learn about cultures but do not learn from them. Read about buddhist teachings but do not become buddhist. Travel but do not assimilate. Preserve but don't share. etc.