hi @Dev-Fox
the resolution you provided above worked.. I just needed to twist it a bit to fit it to my requirement as below

  for( Schema.PicklistEntry OppickListVal : Opple){
            options.add(new selectoption(OppickListVal.getValue(), OppickListVal.getLabel()));}
            
              for(Schema.PicklistEntry ObjpickListVal : Objple){
             options.add(new selectoption(ObjpickListVal.getValue(), ObjpickListVal.getLabel()));}
          
      return options;     


Thank you

Now I want to reflect records from these values based on selection from different the two objects.. any suggestion will be helpful.. below is my current code; its reading only for opportunity and not for vehicles.. thanks

public class Opportunitiesandvehicles{
    public string selectedvalue{set;get;}
    public boolean isclicked{set;get;}
    public boolean flag{set;get;}
    public list<opportunity>  opplist {get;set;}
    public boolean isBool{set;get;}
    public list<vehicle__c> vehiclelist{get;set;}    
    public Opportunitiesandvehicles(){
        isclicked = false;
        isBool = false;
        flag = false;
        opplist = new List<Opportunity>();
        getopvehPickValues();
    }
    
    public List<SelectOption> getopvehPickValues()
    {
        List<SelectOption> options = new List<SelectOption>();
       /* Schema.DescribeFieldResult fieldResult = Account.Industry.getDescribe();

 

        List<Schema.PicklistEntry> ple = fieldResult.getPicklistValues();
        options.add(new SelectOption('','--None--'));
        for(Schema.PicklistEntry f : ple)
        {
            options.add(new SelectOption(f.getLabel(), f.getValue()));
        } */
        
        
        Schema.DescribeFieldResult OppFldResult = Opportunity.Stagename.getDescribe();
        List<Schema.PicklistEntry> Opple = OppFldResult.getPicklistValues();

        Schema.DescribeFieldResult ObjFldResult = Vehicle__c.type__c.getDescribe();
        List<Schema.PicklistEntry> Objple = ObjFldResult.getPicklistValues();

       // list<selectoption> optionLst = new list<selectoption>();
        options.add(new selectoption('', '-None-'));
        for( Schema.PicklistEntry OppickListVal : Opple){
            options.add(new selectoption(OppickListVal.getValue(), OppickListVal.getLabel()));}
            
              for(Schema.PicklistEntry ObjpickListVal : Objple){
             options.add(new selectoption(ObjpickListVal.getValue(), ObjpickListVal.getLabel()));}
          
      return options;       
}
        
        
  
    
    public void searchopportunityRecords(){
        system.debug('sfdc test');
        if(selectedvalue == null || selectedvalue== ''){
            ApexPages.addmessage(new ApexPages.message(ApexPages.severity.FATAL,'Please select value for opportunity or vehicles'));
            isclicked = false;
            isBool = false;
        }
        else{
                system.debug('sfdc test1');
                
                isclicked=true;
                Opplist = [SELECT Id, Name, stagename FROM opportunity Where stagename=:selectedvalue];
                system.debug('opplist = '+opplist.size());
        
            }
            
            if(opplist.size() == 0){
                ApexPages.addmessage(new ApexPages.message(ApexPages.severity.FATAL,'Please pick a value from the piclist above'));
                isclicked = false;
                isBool = true;
            }
     
    }
    
    
    public PageReference displayvehicles() {
        if(selectedvalue!= null){                       
                isclicked=true;
                vehiclelist= [SELECT Id, Name, type__c from Vehicle__c Where type__c=:selectedvalue];
                system.debug('opplist = '+vehiclelist.size());
        
            }
            
            if(vehiclelist.size() == 0){
                ApexPages.addmessage(new ApexPages.message(ApexPages.severity.FATAL,'Please pick a value from the piclist above'));
                isclicked = false;
                isBool = true;
            }
     
     return null;
    }
  
}

_____________________-

<apex:page controller="Opportunitiesandvehicles" id="pg" lightningStylesheets="true">
    
    <style>
        .mypage .quote {
            margin: 12px 0;
            font-size: 32px;
            text-align: center;
        }
        
    </style>
    
    <apex:form id="frm">
        <apex:pageBlock title="Search Criteria" mode="edit">
            <apex:pageBlockSection >
                <apex:selectList size="1" style="width:10%;" value="{!selectedvalue}" styleClass="slds-input">   
                <apex:selectOptions value="{!opvehPickValues}"  /> 
                </apex:selectList> 
                <br/><br/>
                <apex:commandButton value="Show" styleClass="slds-button slds-button_brand" action="{!searchopportunityRecords}"/>
                </apex:pageBlockSection>
                <apex:pageMessages id="showmsg"></apex:pageMessages>
               </apex:pageBlock>        
            <apex:outputpanel rendered="{!isclicked==true}" >
                <apex:pageBlock title="Search Result" mode="edit">
                <apex:pageBlockTable value="{!opplist}" var="Items">
                <apex:column headervalue="Opportunity Name">
                <apex:inputField value="{!Items.Name}"/>
                </apex:column>
                <apex:column headervalue="Opportunity StageName">
                <apex:inputfield value="{!Items.StageName}"/>
                </apex:column>                   
                </apex:pageBlockTable>
                </apex:pageBlock>
         <apex:pageBlock mode="edit" >
                <apex:pageBlockTable value="{!vehiclelist}" var="con" >
                <apex:column headervalue="Vehicle Name">
                 <apex:inputfield value="{!con.Name}"/>
                 </apex:column>
                 <apex:column headervalue="Vehicle Type">
                 <apex:inputfield value="{!con.Type__c}"/>
                 </apex:column>
                 </apex:pageBlockTable>
                 </apex:pageBlock>
            </apex:outputPanel>                       
                 
             
    </apex:form>
</apex:page>