Change it to the following and try it

.fade-enter-active, .fade-leave-active {
    transition: all 1s ease;
}

.fade-enter, .fade-leave-active {
    transform：translateX(100px)
}

Or like this

.erweima{
  position: fixed;
  width: 100px; 
  height: 100px;
  left: 0;
}
.fade-enter-active, .fade-leave-active {
  transition: all 1s ease;

}
.fade-enter, .fade-leave-active {
  left: -100px;
}

Css cannot be written like this. .fade-enter-active, .fade-leave-active classes will be removed after the animation is completed. After removal, it will be your original css style. Therefore, after the animation is executed, 2 The QR code disappeared again

.erweima {//这里需要写最终的显示状态，用v-if或v-show控制

    position: fixed;
    left: -100px;
    bottom: 200px;
}
.fade-enter-active, .fade-leave-active {
    transition: all 1s ease;
    left: -100px;//去掉这句，这个class不是最终状态
}