Is the fact that you're using a bridge at all apparent to your WhatsApp friends? Or is nothing different as far as they are concerned? Also, does Element have a setting to prevent pictures and video from being automatically downloaded over cellular data?
You are better of inviting them to Signal. If they know how to use WhatsApp, then they know how to use Signal. It's designed to be as easy as possible, while secure and private.
That's not how it works on real life. Sure you can invite a handful of people there, but they won't last because their friends aren't there, every one is on WhatsApp
What do you mean by privacy hardened? The messages are going through Facebook's servers, so there's very little you can do in terms of privacy for your conversations. If you want to limit its ability to touch your things on your phone, track you on your phone, be able to use your phone's sensors, etc., then maybe a Matrix bridge or WhatsApp WebToGo on F-Droid? Honestly, I'm interested in a good alternative, because I couldn't get the matrix bridge working several years ago, and WhatsApp WebToGo has issues staying connected and requires a dedicated WhatsApp phone that stays at home or wherever.
Beeper is maybe an alternative. It is basically a matrix bridge. But not only for WhatsApp, also for signal and iMessage and many more. (Now in Beta, later 10$ a month subscription) https://www.beeper.com
There's nothing about Beeper that makes running WhatsApp through it more private. You're still using the Meta platform, but you're adding a new company in the chain. Your messages from the WhatsApp server get decrypted by Beeper then re-encrypted to be sent to you.
There are many modified/modded versions of the official client but I don't think they are "privacy hardened" in any way, they do offer a plethora of extra features though
I use it. It's not great. Basically, you keep a phone at home with WhatsApp installed and running. Then WhatsApp ToGo will connect to it, as though you're connecting from a web browser. And like the web version of WhatsApp, it will occasionally disconnect and require you to resync with the QR.