Thanks for sharing a sandbox! I removed some containers and height settings. The display flex is not useful and not needed here. I see now the banner and the table as full height. Was this your approach?

 <v-app>
    <v-main>
      <div style="height: 50px; background-color: black"></div>
      <v-container fluid>
        <UsersTable :items="users" />
      </v-container>
    </v-main>
  </v-app>