Vue.js - Select / dropdown selected item vm binding is not working (bootstrap-vue)

b-dropdown in bootstrap-vue does not support v-model. As the documentation states:

Dropdowns are toggleable, contextual overlays for displaying lists of links and actions in a dropdown menu format.

In other words, b-dropdown is essentially a UI component for displaying a menu or similar set of options.

I expect what you want is b-form-select.

That said, you could add a click handler to the options that sets the value.

  <b-dropdown-item v-for="option in ddTestVm.options" 
                    :key="option.value" 
                    :value="option.value"
                    @click="ddTestVm.ddTestSelectedOption = option.value">

Here is a working example.