It may be that you're not saving the pictures as jpeg's.
Open the Camera->Settings->Picture Formats->Turn off "High Efficiency Pictures"
Now take a pic and try to send that. The pic will be resized by the Message app and may lose some picture quality.
Galaxy S21 Ultra 512g(VZW), Galaxy Book (original, VZW), Tab S8 Ultra, Tab S4, Galaxy Watch5Pro(VZW), M8 Smart Monitor