I know that Primal doesn't allow private zaps, and I saw that using Wisp only a few people can get private zaps. Does it mean that whatever I sent through Amethyst wasn't private 100%?

just quote the note in a nip 17 dm using a q tag, boom private replies. If you want to show them as replies to the original note that's your business

Nostur TestFlight supports it, giftwrapped kind 1 and kind 1111. I’m showing them in the replies along side public replies