i have sent a passport. i regret it. i got some negligible rewards and passed KYC. it is very unworthy. i won't be stupid again.
I never send international documents like passport for KYC requirements. Some projects ask the identification documents and they later sell this completed data in dark web for money. Very shady and dangerous.
I sent my passport to various projects many times and there is nothing wrong with that. They will not do anything with your documents, so there is nothing special about this. But with the help of KYC, we screen out many unscrupulous participants.