setup.txt / setup.typoscript not being loaded in module - typo3

Question

I'm writing an extensio in Typo3 9.5 and I can't get the setup.txt or setup.typoscript to load.
I am trying to add a second page type that renders only JSON. For that I gather I need to change the typoscript. Therefore I added this code to my setup.typoscript:
ajax_ajaxjson = PAGE
ajax_ajaxjson {
typeNum = 1
config {
disableAllHeaderCode = 1
additionalHeaders = {
10 {
header = Content-Type: application/json
replace = 1
}
}
xhtml_cleaning = 0
debug = 0
no_cache = 1
admPanel = 0
}
10 < tt_content.list.20.tx_energieportal_ajaxjson
}
(in EXT:\Configuration\TypoScript\setup.txt)
Now when trying to load that page type, I get the following error:
TYPO3\CMS\Core\Error\Http\ServiceUnavailableException
The page is not configured! [type=1][]. This means that there is no TypoScript object of type PAGE with typeNum=1 configured.
I also added a test variable, and when rendering that variable with
<f:cObject typoscriptObjectPath="testvar"/>
I get the error:
No Content Object definition found at TypoScript object path "testvar"
I setup my sys_template.php up like this:
<?php
defined('TYPO3_MODE') or die();
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addStaticFile(
'energieportal',
'Configuration/TypoScript',
'Energieportal Frontend'
);
(in EXT:\Configuration\TCA\sys_template.php).
I also tried renaming the setup.txt to setup.typoscript.
Is there anything else I need to do to have my module load the setup.typoscript? I looked at the docs and other modules, but I couldn't find anything for setting up that file.
I used the search function, but the only similar question wasn't really answered. (Link)

Answer 1

If you want to override the TCA of existing tables, you need to put the file into Configuration/TCA/Overrides/.
So, the correct path for your sys_template.php needs to be Configuration/TCA/Overrides/sys_template.php.

Answer 2

\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addStaticFile only adds it to the list of static TypoScript files which can be loaded in a TypoScript template. It does not load the TypoScript file automatically.
You will have to include it in a TypoScript template in the TYPO3 backend. You can find the available static templates in the Includes tab under Include static (from extensions).
Alternatively you can include it in a different TypoScript file that is already loaded in the previously mentioned way using #import 'EXT:EXT:energieportal/Configuration/TypoScript/setup.typoscript' or <INCLUDE_TYPOSCRIPT: source="FILE:EXT:energieportal/Configuration/TypoScript/setup.typoscript">
It is also possible to add TypoScript directly from PHP using \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addTypoScript('My TypoScript'), so you can add the #import or <INCLUDE_TYPOSCRIPT...> line there. You can add this in your extension's ext_localconf.php or Configuration\TCA\Overrides\sys_template.php. It is however usually not recommended as you might not want the TypoScript loaded for all pages and/or sites in a TYPO3 installation.