A lot of iPhone users are having issues with the Messages app, and most of the complaints reportedly come from iPhone 12 owners.
A couple of solutions have been proposed by affected users, such as downloading the Verizon Message+ app if you are on Verizon, or resetting network settings, but they do not work for everyone.
Apple Support has reportedly told some users that this is a carrier issue. The problem will likely be fixed with a software update.
Here is what one user had to say regarding the messages bug: