I have the same issue everyone is reporting here. I have the iPhone 8 Plus and am on ios 14.2. Latest update stopped messages from notifying me from several different apps, including Mail, Facebook, Facebook Messenger, Twitter...etc.
I am really unhappy that this change was made in the release. It's extremely inconvenient. Because I'm not getting notifications I have potention employers calling me and asking if I received their email with job descriptions...etc. Because I don't watch email all day non-stop, I can sometimes go hours without checking email and have missed some urgent stuff.
Apple: Please undo this for us, or create a way for people to choose whether they wish to use this part of the update or not.