DE has states listed by postal abbr, but selection list does not. Pre-populate state in selection and disable selection list.

SelectStateAndDisabled.ampscript

%%[
SET @finalState = deStateValue
]%%
  
  <form id="SubmitRegistration" action="%%=CloudPagesURL('111')=%%" method="post">

    <select class="inputBox state" id="" name="formState" title="State" %%=IIF(EMPTY(@finalState),'','disabled')=%%>
     <option value="">--</option>
          <option value="Alabama" %%=IIF(@finalState == 'AL','Selected','')=%%>Alabama</option>
          <option value="Alaska" %%=IIF(@finalState == 'AK','Selected','')=%%>Alaska</option>
          <option value="Arizona" %%=IIF(@finalState == 'AZ','Selected','')=%%>Arizona</option>
          <option value="Arkansas" %%=IIF(@finalState == 'AR','Selected','')=%%>Arkansas</option>
          <option value="California" %%=IIF(@finalState == 'CA','Selected','')=%%>California</option>
          <option value="Colorado" %%=IIF(@finalState == 'CO','Selected','')=%%>Colorado</option>
          <option value="Connecticut" %%=IIF(@finalState == 'CT','Selected','')=%%>Connecticut</option>
          <option value="Delaware" %%=IIF(@finalState == 'DE','Selected','')=%%>Delaware</option>
          <option value="District of Columbia" %%=IIF(@finalState == 'DC','Selected','')=%%>District of Columbia</option>
          <option value="Florida" %%=IIF(@finalState == 'FL','Selected','')=%%>Florida</option>
          <option value="Georgia" %%=IIF(@finalState == 'GA','Selected','')=%%>Georgia</option>
          <option value="Hawaii" %%=IIF(@finalState == 'HI','Selected','')=%%>Hawaii</option>
          <option value="Idaho" %%=IIF(@finalState == 'ID','Selected','')=%%>Idaho</option>
          <option value="Illinois" %%=IIF(@finalState == 'IL','Selected','')=%%>Illinois</option>
          <option value="Indiana" %%=IIF(@finalState == 'IN','Selected','')=%%>Indiana</option>
          <option value="Iowa" %%=IIF(@finalState == 'IA','Selected','')=%%>Iowa</option>
          <option value="Kansas" %%=IIF(@finalState == 'KS','Selected','')=%%>Kansas</option>
          <option value="Kentucky" %%=IIF(@finalState == 'KY','Selected','')=%%>Kentucky</option>
          <option value="Louisiana" %%=IIF(@finalState == 'LA','Selected','')=%%>Louisiana</option>
          <option value="Maine" %%=IIF(@finalState == 'ME','Selected','')=%%>Maine</option>
          <option value="Maryland %%=IIF(@finalState == 'MD','Selected','')=%%">Maryland</option>
          <option value="Massachusetts" %%=IIF(@finalState == 'MA','Selected','')=%%>Massachusetts</option>
          <option value="Michigan" %%=IIF(@finalState == 'MI','Selected','')=%%>Michigan</option>
          <option value="Minnesota" %%=IIF(@finalState == 'MN','Selected','')=%%>Minnesota</option>
          <option value="Mississippi" %%=IIF(@finalState == 'MS','Selected','')=%%>Mississippi</option>
          <option value="Missouri" %%=IIF(@finalState == 'MO','Selected','')=%%>Missouri</option>
          <option value="Montana" %%=IIF(@finalState == 'MT','Selected','')=%%>Montana</option>
          <option value="Nebraska" %%=IIF(@finalState == 'NE','Selected','')=%%>Nebraska</option>
          <option value="Nevada" %%=IIF(@finalState == 'NV','Selected','')=%%>Nevada</option>
          <option value="New Hampshire" %%=IIF(@finalState == 'NH','Selected','')=%%>New Hampshire</option>
          <option value="New Jersey" %%=IIF(@finalState == 'NJ','Selected','')=%%>New Jersey</option>
          <option value="New Mexico" %%=IIF(@finalState == 'NM','Selected','')=%%>New Mexico</option>
          <option value="New York" %%=IIF(@finalState == 'NY','Selected','')=%%>New York</option>
          <option value="North Carolina" %%=IIF(@finalState == 'NC','Selected','')=%%>North Carolina</option>
          <option value="North Dakota" %%=IIF(@finalState == 'ND','Selected','')=%%>North Dakota</option>
          <option value="Ohio" %%=IIF(@finalState == 'OH','Selected','')=%%>Ohio</option>
          <option value="Oklahoma" %%=IIF(@finalState == 'OK','Selected','')=%%>Oklahoma</option>
          <option value="Oregon" %%=IIF(@finalState == 'OR','Selected','')=%%>Oregon</option>
          <option value="Pennsylvania" %%=IIF(@finalState == 'PA','Selected','')=%%>Pennsylvania</option>
          <option value="Rhode Island" %%=IIF(@finalState == 'RI','Selected','')=%%>Rhode Island</option>
          <option value="South Carolina" %%=IIF(@finalState == 'SC','Selected','')=%%>South Carolina</option>
          <option value="South Dakota" %%=IIF(@finalState == 'SD','Selected','')=%%>South Dakota</option>
          <option value="Tennessee" %%=IIF(@finalState == 'TN','Selected','')=%%>Tennessee</option>
          <option value="Texas" %%=IIF(@finalState == 'TX','Selected','')=%%>Texas</option>
          <option value="Utah" %%=IIF(@finalState == 'UT','Selected','')=%%>Utah</option>
          <option value="Vermont" %%=IIF(@finalState == 'VT','Selected','')=%%>Vermont</option>
          <option value="Virginia" %%=IIF(@finalState == 'VA','Selected','')=%%>Virginia</option>
          <option value="Washington" %%=IIF(@finalState == 'WA','Selected','')=%%>Washington</option>
          <option value="West Virginia" %%=IIF(@finalState == 'WV','Selected','')=%%>West Virginia</option>
          <option value="Wisconsin" %%=IIF(@finalState == 'WI','Selected','')=%%>Wisconsin</option>
          <option value="Wyoming" %%=IIF(@finalState == 'WY','Selected','')=%%>Wyoming</option>
    </select>

     <button class="button buttonSubmit" type="submit" form="SubmitRegistration" name="SubmitRegistration" value="SubmitRegistration"><span class="label">Submit</span>
                   </button>
  
  </form>