I fell for a feint though. Reading their docs it seemed like they were going to go in the direction of class components with attributes (class decorators). So we built our app for that, thinking we'd be future proof, but alas the community went 180 degrees the other way, and our Vue 2 app became super hard to upgrade to Vue 3.
Without more context can't comment on your upgrade process. But as others stated above, there's not much difference betweeb 2 and 3, except you do not get composition api on a v2 project, while you can use composables but can't go full composition api and have to stick to options api. Other than that most of v2 code would work on v3.
