foundry/Data/systems/pf2e/templates/items/action-sidebar.hbs

<div class="inventory-details">
    <div class="form-group">
        <label>{{localize "PF2E.Category"}}</label>
        <select name="system.category">
            {{#select data.category}}
                <option value="">{{localize "PF2E.Item.Action.Category.None"}}</option>
                {{#each categories as |name type|}}
                    <option value="{{type}}">{{localize name}}</option>
                {{/each}}
            {{/select}}
        </select>
    </div>
</div>