If your Messages by Google Beta app is crashing on an Android 14 Beta release, you should uninstall the former
But if you already installed the latest version of the Messages by Google Beta, there is a way to undo the damage. Long-press the Messages icon on your home screen and tap the info icon (the “i” inside the circle on the left of the top lozenge). You’ll be sent to the App info page for the Messages app. Tap the three-dot overflow icon in the upper right and you’ll see an option to Uninstall updates. Tap on it and you should have the latest Messages by Google Beta update removed. This should allow RCS chat to work again on the Android 14 Beta.
Besides uninstalling the Messages by Google beta from your phone, you could choose to exit the Android 14 Beta program early. But if you do this, you will have to wipe all of the data off of your phone which is something that you probably don’t want to do unless you backed up everything. With that in mind, your best bet is to uninstall the latest version of the Messages by Google beta app following the directions laid out two paragraphs to the North.