Okay. Cultural Appropriation. This is a big, touchy topic.
I, to, am Norwegian (and Swedish, and a bit Danish). I'm also American, and was raised in a Christian religion, but my Norwegian ancestry is a not-insignificant part of my identity. My grandparents on my father's side (especially my grandfather) were both super into ancestry and family history, and I can tell you the story of how my family came across the Atlantic to America, were split up due to the immigration system, and although the long-lost siblings were never able to meet each other again in the USA, how their children were able to all come together again and keep in touch so that they'd never be lost again. I can tell you how my many-generations-back-Grandfather (whom I share a middle name with) was converted to Protestantism and how he emigrated to the USA from Norway to avoid religious persecution, while still keeping his Norse heritage a part of his identity. I'm descended from Vikings and Norse Kings (including the amusingly named "Olaf Olafsson", and another, "Olaf, King of Farts"), and my Grandfather would take me to local Norwegian Heritage clubs and make me eat
Lutefisk (god, it tastes awful. For those that don't know, it's basically jello made of fish). I grew up on stories about Thor, Loki, Odin, Fenris Wolf, Dwarves, Elves, Einherjar, Valkyries, the Vanir, Aesir, and Jötunns.
I obviously cannot speak for all people of Norse heritage, especially those that still practice the worship of Norse deities, and I definitely cannot speak for members of other cultures and their views of cultural appropriation vs. appreciation, but when I see someone like Rick Riordan using my ancestral culture in his
Magnus Chase and the Gods of Asgard series, I smile with glee. Cultural appropriation is not a concern of mine. Yes, he is gaining wealth and status from the use of my ancestry's culture, which with an Irish name like Riordan, he likely doesn't belong to, but I have no more ownership of my ancestors' culture than he does, and the form that he uses Norse mythology in is largely positive (yes, some of the gods are played for laughs, like Heimdall and Thor, but it's still spreading an overall-positive tone on Norse Mythology and I don't get offended by how those gods are portrayed), which has an overall positive effect on how people view/feel about my ancestral culture. It certainly is a good use of Norse mythology and runes,
which is more than I can say for another (very infamous) modern usage of Norse runes and culture. (Obviously the line to determine "is this a bad way to use a part of another culture" isn't "it's fine if they're not white supremacists", I'm just pointing out that there are layers of appropriation and more nuance than it always being "that's
my culture! You can't have/use it!")
I love Greek mythology. I feel no guilt using aspects of Greek mythology in my games (Satyrs, Griffons, Pegasi, Dryads and other Nymphs, Centaurs, Drakons, etc), as well as certain parts of other cultures (I have a Gargantuan Couatl in my games called the "Quetzalcouatl" from Aztec/Mayan mythology, I have Tiamat and Bahamut like the base game does, I use many parts of the bits and pieces of other languages that I know to form the languages of my worlds, and so on). IMO, using parts of different cultures is more often Cultural Appreciation than Cultural Appropriation. I typically see something as Cultural Appropriation when they take a part of another culture and claim it as their own without recognizing or appreciating its roots. If I said "I invented
Quetzalcoatl, give me money and/or credit in order to use him and all names associated with him", that would be Cultural Appropriation. If I instead said, "Here's a cool D&D celestial creature that is a flying snake with feathers, known as Quetzalcoatl, inspired by the deity from Aztec and Mayan mythologies", IMO, that's not cultural appropriation (or at least not a negative form of it), it's appreciating the amazing and awesome parts of cultures around the world. I would feel the same way if someone took Thor and turned him into an awesome god-hero in a Superhero Cinematic Universe (it would be a Marvel if that happened, wouldn't it?).
That's just my two cents, though.