Zendesk Nesty input customization

gistfile1.js

// Remove the option from the select element
    $('#<complete_zendesk_form_field_id> option[value="<zendesk_dropdown_value_tag>"]').remove();
    
    // Callback function to execute when mutations are observed
    const callback = function(mutationsList, observer) {
        for(let mutation of mutationsList) {
            if (mutation.type === 'childList') {
                // Remove the option from the nesty-input after it's been created
                $('.nesty-panel').children('ul').children().remove('#<zendesk_dropdown_value_tag>');
            }
        }
    };

const buildingFieldEle = document.querySelector('.request_custom_fields_21512039916189');
    const buildingNestyInput = buildingFieldEle.querySelector('a.nesty-input');
    const buildingNestyInputPanel = document.querySelector(`.nesty-panel#${buildingNestyInput.getAttribute('aria-controls')}`);
    let panelOpen = false;

    // Callback function to execute when mutations are observed
    const callback = function(mutationsList, observer) {
        for(let mutation of mutationsList) {
            if (mutation.type === 'childList') {
                if(!panelOpen) {
                  const elementToSelect = $('.nesty-panel').children('ul').children('li.nesty-expand')[0];
                  if((!mutation.previousSibling && !mutation.removedNodes.length ) && elementToSelect && !panelOpen) {
                    elementToSelect.click();
                    panelOpen = true;
                  }
                }
                else if (mutation.removedNodes.length > 0 && !mutation.target.querySelector('ul')) {
                  panelOpen = false;
                }
            }
        }
    };
    
    // Create an observer instance linked to the callback function
    const observer = new MutationObserver(callback);
    
    // Start observing the target node for configured mutations
    observer.observe(buildingNestyInputPanel, { childList: true });

for nested fields first get all the nest panels

var skip1 = document.querySelectorAll('.nesty-panel')

Then watch for every time the panel is inserted to the DOM and remove the options by tag you don't need

$(skip1).on('DOMNodeInserted', function(e){$(this).children('ul').children().remove('#nest__two_2');})