Why specific icon is not working on append-icon?

In my entire vuejs project, I can use any icons from here

https://fonts.google.com/icons?selected=Material+Icons

Lately, I am trying out append-icon, as you can see at

append-icon=”folder”

Proof

calendar_month is a proper spelling of that icon

https://fonts.google.com/icons?selected=Material+Icons&icon.query=calendar_month

Codes

<v-col class="col-sm-4 col-lg-4 col-4">
    <v-text-field
        append-icon="folder"
        class="mb-5"
        v-model="timezone"
        :rules="timezoneRules"
        label="Timezone"
        required
    ></v-text-field>
</v-col>

<v-col class="col-sm-4 col-lg-4 col-4">
    <v-text-field
        append-icon="calendar_month"
        class="mb-5"
        v-model="startDate"
        :rules="startDateRules"
        label="startDate"
        required
    ></v-text-field>
</v-col>

Result

enter image description here

Why only folder works ? Did I do sth wrong ?