Default checked checkbox not working in angular

I tried almost all ways checked,checked="true",[checked]="true" and tried different answers like this one on stackoverflow but not working for me

    <ng-template #content>

    <label class="switch">
        <input  type="checkbox" name=""  ngModel required #="ngModel"  [checked]="true"  checked="true">
        <span class="slider round"></span>
    </label>
</ng-template>

<ng-template #other_content>

    <label class="switch">
        <input type="checkbox" name="" ngModel required #="ngModel">
        <span class="slider round"></span>
    </label>
</ng-template>