After installing the Vue.js devtools, I opened the vue webpage I wrote and found that the vue icon in the upper right corner was gray, and there was no Vue option when opening the console through F12.
Inquiry through the Internet: The
most mentioned are to open the Vue extension, enable incognito mode (privacy mode), and allow access to file URLs, these two items.
For your own is still useless, click the Vue icon with the left mouse button (the extension has fixed Vue to the page), and a prompt text will appear.
Case 1: 
Vue.js not detected, the Vue icon is gray, this situation can usually be solved by the above method.
Case 2: The 
Vue icon is highlighted, but there is no Vue project in the console. The key information in this situation is that "because it's in production mode"
needs to change the development environment of webpack from "production" to "development". You can refer to this man.
If it still doesn't work: open the vue plugin installation location, open mainifest.json,
Change persistent: false in mainfest.json to persistent: true.
By the time I got here, mine was ready.
When Vue can appear in the console, click the vue icon in the upper right corner, the prompt is: The
above content is for reference only, and everyone is welcome to discuss.