A new layout for Google Messages that integrated the gallery and camera was widely released in June. When you tapped the button to the right of the text box, a grid appeared underneath and a viewfinder at the top. When attaching an image, some folks didn't want to turn on their camera each time. (Disabling the app's camera was one remedy.)
Google is starting to provide a method to access each separately after hearing the feedback. A new stand-alone "Camera" option appears in the grid when you tap the "plus" menu on the right. "Gallery" just launches the photo picker and receives an updated camera-less icon.
Together with GIFs, Stickers, Magic Compose, Files, Location, Contacts, Schedule Send, and Selfie GIF, they are the first two options in the menu, which has ten things altogether.
According to the one story we have of this change, which is taking place on top of the Material 3 Expressive redesign, Google is likely maintaining the symbol in the text field as the default, which still launches the unified interface. Although the new approach involves an additional step, it resolves the main issue.
This hasn't been widely released on handsets running the most recent Google Messages beta as of yet.