fieldAccessExplorer.css

/* parent.css */
divcenter {
        text-align: center;
}
.divSize
{
        height: 400px;
}

fieldAccessExplorer.html

<template>
        <div>
                <lightning-card class="divSize"> 
                <div style="text-align: center;">SalesforceCodex Field's Access Explorer</div>
        
                <lightning-layout multiple-rows>
                        <lightning-layout-item size="2" padding="around-small">
                                                <lightning-combobox
                                                name="Users"
                                                label="Users"
                                                value=""
                                                placeholder="Select User"
                                                options={users}
                                                onchange={handleUserChange}
                                                required
                         >
                        </lightning-combobox>
                        </lightning-layout-item>
                        <lightning-layout-item size="2" padding="around-small">
                                <lightning-combobox name="objectName" 
                                label="Object"
                                value="" 
                                placeholder="Select Object" 
                                options={objects} 
                                onchange={handleObjectChange}
                                required></lightning-combobox>
                        </lightning-layout-item>
                         <lightning-layout-item size="2" padding="around-small">
                                <lightning-combobox
                                name="Fields"
                                label="Fields"
                                value=""
                                placeholder="Select Field"
                                options={fields}
                                onchange={handleFieldChange}
                        ></lightning-combobox> 
                         </lightning-layout-item>
                        
                        <lightning-layout-item size="4" padding="around-small">
                                <div class="slds-m-around--medium">
                                <lightning-button label="Get Users Access" title="Get Users Access" onclick={handleClick}>
                                </lightning-button>
                                </div>
                        </lightning-layout-item>
                </lightning-layout>
                </lightning-card>
                <lightning-card title="Field Access">
                        <br />
                        <div style="width: auto;">
                              <lightning-datatable data={data}
                                                   columns={columns}
                                                   key-field="Id">
                              </lightning-datatable>
                  
                        </div>
                      </lightning-card>
        </div>
</template>

fieldAccessExplorer.js

import { LightningElement, track, wire} from 'lwc';
import getObjects from '@salesforce/apex/FieldExplorerController.getObjects';
import getFields from '@salesforce/apex/FieldExplorerController.getFields';
import getObjectAccess from '@salesforce/apex/FieldExplorerController.getObjectAccess';
import getFieldsAccess from '@salesforce/apex/FieldExplorerController.getFieldsAccess';
import getOrgUsers from '@salesforce/apex/FieldExplorerController.getOrgUsers';

const columnsDefs = [
    {
        label: 'EntityDefinitionId',
        fieldName: 'EntityDefinitionId',
        type: 'text',
        sortable: true
    },
    {
        label: 'FieldDefinitionId',
        fieldName: 'FieldDefinitionId',
        type: 'text',
        sortable: true
    },

    {
        label: 'FieldName',
        fieldName: 'FieldName',
        type: 'text',
        sortable: true
    },
    {
        label: 'IsAccessible',
        fieldName: 'IsAccessible',
        type: 'boolean',
        sortable: true
    },
    {
        label: 'IsUpdatable',
        fieldName: 'IsUpdatable',
        type: 'boolean',
        sortable: true
    },
    {
        label: 'IsCreatable',
        fieldName: 'IsCreatable',
        type: 'boolean',
        sortable: true
    }
];

export default class FieldAccessExplorer extends LightningElement {
    @track objects = [];
    @track fields = [];
    @track users = [];

    @track field='';
    @track objName='';
    @track user='';
    @track data;
    @track columns = columnsDefs;
    connectedCallback()
    {
        getOrgUsers()
        .then(result => {
            this.dataArray = result;
            let tempArray = [];
            this.dataArray.forEach(function (element) {
                var option=
                {
                    label:element.Name,
                    value:element.Id
                };
                tempArray.push(option);
            });
            this.users=tempArray;
            console.log(this.users);
        })
        .catch(error => {
            this.error = error;
        });
    }

    @wire(getObjects)
    wiredMethod({ error, data }) {
        if (data) {
            this.dataArray = data;
            let tempArray = [];
            this.dataArray.forEach(function (element) {
                var option=
                {
                    label:element,
                    value:element
                };
                tempArray.push(option);
            });
            this.objects=tempArray;
        } else if (error) {
            this.error = error;
        }
    } 

    
    handleObjectChange(event)
    {   
        const selectedOption = event.detail.value;  
        this.objName=selectedOption;

        getFields({ objectName: selectedOption})
        .then(result => {
            this.dataArray = result;
            let tempArray = [];
            let option=
                {
                    label:'Please Select',
                    value:''
                };
            tempArray.push(option);
            this.dataArray.forEach(function (element) {
                option=
                {
                    label:element.Label,
                    value:element.Name
                };
                tempArray.push(option);
            });
            this.fields=tempArray;
        })
        .catch(error => {
            this.error = error;
        });

    }
    handleFieldChange(event){
        const selectedOption = event.detail.value;  
        this.field=selectedOption;
    }
    handleUserChange(event){
        const selectedOption = event.detail.value;  
        this.user=selectedOption;
    }

    handleClick(){       
        if(this.field==='')
        {
            getObjectAccess({ objectName: this.objName,userId:this.user})
            .then(result => {
                this.data=result;
            })
            .catch(error => {
                console.log('Error'+ JSON.stringify(error));
                this.error = error;
            });
        }
        else
        {
            getFieldsAccess({ objectName: this.objName,fieldName:this.field,userId:this.user})
            .then(result => {
                this.data=result;
            })
            .catch(error => {
                console.log('Error'+ JSON.stringify(error));
                this.error = error;
            });
        }
    }
}

fieldAccessExplorer.js-meta.xml

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata" fqn="fieldAccessExplorer">
    <apiVersion>47.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightningCommunity__Page</target>
        <target>lightningCommunity__Default</target>
        <target>lightning__RecordPage</target>
        <target>lightning__AppPage</target>
        <target>lightning__HomePage</target>
    </targets>
</LightningComponentBundle>