Samsung seem to think that selfie cameras should work as mirrored, and I can't see any way of turning that off for the preview (I had to look because I never take selfies so didn't know what options there were for the front camera). On my s21 turning off the "save picture as previewed" does make it save correctly (i.e. not mirrored), so I don't know why that doesn't work for you. For selfies you could probably fix this by using a different camera app.

For video in other apps it may depend on whether they have an option of their own. For example you can turn mirroring off in Zoom's video settings, but I can't see anything in WhatsApp's (very limited) settings. I get the impression that Samsung have made mirrored the default and so a third party app will need to undo that, which is probably more effort than most will put in. For things like holding up something with writing the best solution is probably to just switch to the main camera to show people stuff.

It is stupid that they force the stupid option on video, but it's odd that the option to turn it off doesn't work with your camera app.

 

This is all I could find yesterday. Possibly there's two options to flip before saving. IDK

https://www.samsung.com/us/support/answer/ANS00086762/