I don't know about WhatsApp, but Signal doesn't meet my definition of "social media."
Anyway, Signal doesn't approve use of the third-party clients. Tough luck. Dumb-phone-with-Signal has to be a collaboration with Signal-the-company.
Congratulations, you made my skin crawl.
I'm quite familiar with Signals opposition to third-party clients. I maintained my own fork of their app for about a year in order to keep SMS support. Eventually my fork got so wildly out-of-sync with upstream that I just couldn't keep up anymore.
Why /s?
Stories is exactly an example of a feature being toxic (especially, but not exclusively) for children.