[Vuejs]-Why does accessing a reactive variable not work in my Vue-app (trying to implement a dark mode in Vue)?

Explaining it, I have found the reason. It was because I always entered the corresponding page into the URL of my browser. /register vs. /home … when clicking on a RouterLink, for example:

<RouterLink to="/register">Register</RouterLink>

It worked, the app remembered the correct value. :/ Stupid me.