[SalesForce] LWC ComboBox Cannot Select Option

you can declare a 'hasDefault' getter in your controller and in your template, if:true, render a default result option:

    <template if:true={bears.data}>
            <div class="slds-m-around_medium">

                <select class="slds-select" onchange={handleBearView} >

                         <!-- HERE Check for default value -->
                        <template if:true={hasDefaultResults}> 
                            <option value={hasDefaultResults.Id}>{hasDefaultResults.Name}</option>
                        </template>

                       <template  for:each={bears.data} for:item="bear">
                            <option key={bear.Id} value={bear.Id} >{bear.Name}</option>
                        </template>
                   </select> 
            </div>
    </template>

and create a getter:

get hasDefaultResults() {
        //check if array has data
        if(this.bears.data.length > 0){
              //here as an example, i set the second element from 
              //the array as the default, this can be whatever you want
            return (this.bears.data[1]);
        }

Note: this will generate a duplicate value, so, you will have to figure out a way to exclude it from your original array, either in the template or in your controller.

This cannot be achieved through wired property. You should be using wired function as below:

@track value = '';
@track StatePicklistValues;
@wire(getPicklistValues, {
    recordTypeId: '$objectInfo.data.defaultRecordTypeId',
    fieldApiName: STATE_FIELD
})
getStatePicklistValues(result) {
    if (result.data) {
        console.log(JSON.stringify(result.data));
        this.StatePicklistValues = [ { label: 'Select State', value: '', selected: true }, ...result.data.values ];
    } else if (result.error) {
        alert('ERROR');
    }
}

For sorting, you can do custom sort as follows while assigning:

...result.data.values.sort(function(a, b){return // custom logic});

Note: You should remove placeholder from combobox