As of this post creation, Vue.js version 3 is available, and is “being promoted” over version 2. For example, the default “npm install -g @vue/cli” install will use Vue 3.2.41 by default.
Don’t use version 3 at this time.
The reason: Vue.js v3.0 was released 2020/Sep. But Vue.js v3.2 was released 2021/Aug, and there is some sort of “architecture war” (negative spin) or “massive improvement” (positive spin) happening with v3.2
Specifically – v3.2 has introduced <script setup> coding style, which results in “… difference in module execution semantics”. The documentation and examples for <script setup> is very thin, and seems to (typically) assume you already know how to use it while it is being explained.
Just stick with Vue.js (v2.5 is what I’m using in “compatibility mode” with “vue init” from the Vue CLI tool suite. After my application is fully functional, I’ll try to upgrade to v2.7 (which is EOL 2023/Dec; hopefully a year from now v3.2 will have caught up in its documentation.)