When digging deeper into the error message, I was presented with a 404 page from the firewall and that certificate was self signed - of course.

That's why I set up the cloudron unbound to use the dns of my firewall as described here: https://docs.cloudron.io/troubleshooting/#dns and now the curl operation works as expected. The topic can now be closed. Thank you all for your help and pointing me to the right directions!

Yes, it shows the correct public IP of the domain.

Both web terminals do that correctly. But when it comes to curl, the "self signed certificate" error shows up.

In the Web terminal of the app, can you host krisenkompass.de ? Does it point to your IP correctly?

Both wordpress apps are installed on the same cloudron server. (I have two cloudron servers btw. and both are running for over a year now. One is older than the other. The Wordpress apps are running on the "younger" one). For Wordpress I use the WPAllImport/WPAllExport Plugind by Soflyy. I used those for years now on my old servers. Now I switched with these two domains/apps to the cloudron server and I get these errors.

Maybe there is something else not working correctly, as I cannot "Renew Certs" as you mentioned. Each click ends in an
Cannot read properties of undefined (reading 'WEBSOCKETS_DOMAIN') error. I'll dig into this first, maybe that is the source, why I cannot curl wordpress on that cloudron instance.

This is from the Log view:

Jul 30 16:37:39 box:tasks setCompleted - 4772: {"result":null,"error":{"stack":"TypeError: Cannot read properties of undefined (reading 'WEBSOCKETS_DOMAIN')\n at writeAppLocationNginxConfig (/home/yellowtent/box/src/reverseproxy.js:550:47)\n at process.processTicksAndRejections (node:internal/process/task_queues:95:5)\n at async writeAppConfigs (/home/yellowtent/box/src/reverseproxy.js:573:9)\n at async checkCerts (/home/yellowtent/box/src/reverseproxy.js:682:13)","message":"Cannot read properties of undefined (reading 'WEBSOCKETS_DOMAIN')"}}
Jul 30 16:37:39 box:tasks update 4772: {"percent":100,"result":null,"error":{"stack":"TypeError: Cannot read properties of undefined (reading 'WEBSOCKETS_DOMAIN')\n at writeAppLocationNginxConfig (/home/yellowtent/box/src/reverseproxy.js:550:47)\n at process.processTicksAndRejections (node:internal/process/task_queues:95:5)\n at async writeAppConfigs (/home/yellowtent/box/src/reverseproxy.js:573:9)\n at async checkCerts (/home/yellowtent/box/src/reverseproxy.js:682:13)","message":"Cannot read properties of undefined (reading 'WEBSOCKETS_DOMAIN')"}}
[no timestamp]  Cannot read properties of undefined (reading 'WEBSOCKETS_DOMAIN')
[no timestamp]  at writeAppLocationNginxConfig (/home/yellowtent/box/src/reverseproxy.js:550:47)
[no timestamp]  at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
[no timestamp]  at async writeAppConfigs (/home/yellowtent/box/src/reverseproxy.js:573:9)
[no timestamp]  at async checkCerts (/home/yellowtent/box/src/reverseproxy.js:682:13)

[Edit: The "Renew certs" now works again. I had tested the pixelfed app on that instance as well and there were some problems with the certification process. This has been fixed now.]

As for the CURL-Operations:
The importer tries to CURL the images from the exported website to the other one. Therefore it tries to CURL the images. Tage this one for example:
https://krisenkompass.de/wp-content/uploads/2024/06/Dank-Allen.jpg

When I open the terminal of the wordpress app where this shall be imported and try to run the CURL task manually

https://krisenkompass.de/wp-content/uploads/2024/06/Dank-Allen.jpg

I receibe the following error message:

curl: (60) SSL certificate problem: self-signed certificate
More details here: https://curl.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.

I know, there had been troubles with let's encrypt and wordpress and I checked and replaced the ca-certs-file within wordpress already (though the terminal does not even use the wordpress ca-certs file, so I guess it makes use of the OSs ca-certs).

On Cloudron, the certificates are managed by nginx. This is in front of the application and the application has no idea about it. Any cert changes you make inside the WordPress container has no effect.

When I try to curl the file in the terminal of an app, I also get this error.

Can you tell us more about this? Are you trying to cURL an external app ? Are you transfering between WP instances where both are hosted on Cloudron ?