I don't know what you mean by a "widget" for WhatsApp (the camera button in the message entry field isn't a widget, but it's the only thing I can think of). The way to get a choice of lenses etc is to take the photos first, then share them via WhatsApp: either select share from your gallery app or else use the paperclip icon in the WhatsApp message entry field to select and add them to a message. That's how I normally work, and while there is downscaling and compression the photo quality at least is still better than a screen shot (I find video quality OK for phone usage, though if you compare side-by-side with the original you can see that it's more compressed). There is a photo quality setting, but I don't know whether that affects video (I don't send a lot of videos, and generally don't need the highest quality for sharing stuff this way: I'd email the original, or upload it and share the link, if I wanted that).
Signal has media quality settings (standard and high), but I've never used it for sending media so don't know about what that means in practice. The problem with any of these apps is that you need to persuade everyone you want to send to to sign up.
Another option is to use something like Google photos, create a gallery for stuff you want to share and share that with people. That will allow you to share with higher quality, but doesn't have the convenience of being integrated with message threads. As with anything, there's a trade-off between quality and convenience in these things.
