When I click Launch centered modal, I expect the modal hide the buttons x,cancel and ok because showButton is false.

After I click the show button, the button of the modal should be shown because now showButton is true.

How should I do it?

App.vue

<template>
  <div id="app">
    <b-button v-b-modal.modal-center>Launch centered modal</b-button>
    <b-modal id="modal-center" centered title="BootstrapVue">
      <p class="my-4">Vertically centered modal!</p>
      <button @click="setShowButton">Show Button</button>
    </b-modal>
  </div>
</template>

<script>
export default {
  name: "App",
  data() {
    return {
      showButton: false,
    };
  },
  methods: {
    setShowButton() {
      this.showButton = true;
    },
  },
};
</script>

<style>
#app {
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}
</style>

Codesandbox
https://codesandbox.io/s/flamboyant-herschel-62wpt?file=/src/App.vue:0-587