Disable field in TCA when editing a record - typo3

Question

Is it possible to disable a field in the TCA config, only when editing a record?
TCA config for new record:
'title' => [
'exclude' => true,
'label' => 'Title',
'config' => [
'type' => 'input',
'size' => 30,
'eval' => 'trim,required'
],
],
TCA config for existing records:
'title' => [
'exclude' => true,
'label' => 'Title',
'config' => [
'type' => 'input',
'size' => 30,
'eval' => 'trim,required'
'readOnly' => true,
],
],

Answer 1

I'm not aware of a built in solution for different TCA settings for new and existing records.
Since the final TCA is cached there is also no way to manipulate it with some PHP on runtime.

Answer 2

It is possible to add Javascript in the backend. With this Javascript your are able, to disable fields on the fly. But be aware, that this is just a hacky workaround which can easily be overcome!
Add Javascript in ext_localconf.php:
if (TYPO3_MODE === 'BE') {
$renderer = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Core\Page\PageRenderer::class);
$renderer->addJsFile(
'EXT:myext/Resources/Public/JavaScript/Backend.js'
);
}
In Backend.js you can do something like this:
require(["jquery"], function ($) {
const queryString = decodeURI(window.location.search),
urlParams = new URLSearchParams(queryString);
if (urlParams.has('route') && urlParams.get('route') == '/record/edit') {
// check, that you just do changes, if you edit records of the desired model
if (queryString.indexOf('edit[tx_myextension_domain_model_model][')) {
let idPosStart = queryString.indexOf('edit[tx_myextension_domain_model_model][') + 40,
idPosEnd = queryString.indexOf(']=', idPosStart),
idLength = idPosEnd - idPosStart,
idEl = queryString.substr(idPosStart, idLength),
elVal = urlParams.get('edit[tx_myextension_domain_model_model][' + idEl + ']');
if (elVal == 'edit') {
// Delay everything a little bit, otherwise html is not fully loaded and can't be addressed
setTimeout(function () {
// disable desired fields, eg field "title"
let titleField = $('[data-field="title"]').parents('.form-section');
titleField.find('input').prop('disabled', true);
titleField.find('button.close').remove();
}, 800);
}
}
}
}