I have read that a "Demand letter for return of property" can be sent to Poloniex. It should also be possible to fill it out online.
I am European. Can I also use this letter?
Has anyone already had experience with this or any other method these days?
Has anyone been able to convert or transfer DAOs from Poloniex in the last few months?
You may as well try your demand of property letter. It most likely will be responded to and it'll be irrelevant that you're in a different jurisdiction as it's something they still have to follow in theirs.