It depends on if you trust Meta. Generally speaking there is end-to-end encryption in WhatsApp, which means only you and the person you chat with can decrypt your messages / media (source). I believe there are some weak spots in group chats, mostly caused by users themselves. Not sure about the new Community function but I’d be careful with what I share there.
Some parties like Apple have decided to scan photos from your device for illegal material. If using an app like WhatsApp I’d personally be aware that something like that might happen in the future as well. I’d not be surprised if some employees might (temporarily) be able to access more data than widely assumed, for debugging reasons in case of bugs.
Personally I take the risk for pragmatic reasons, but it doesn’t hurt to be a bit cautious / aware.
Sharing ideas can definitely be worth something when it leads to something actual original/concrete/useful, but on another level.
Most ideas these “creatives” come up with are neither of those + they are not willing to put in some effort to solidify the idea themselves.