AWS Amplify add custom domain not possible because top level domain (tld) is not supported.

Hello, I have setup an Amplify App and want to configure a custom domain. Working with Amplify for around 2 weeks I have seen that the console ui has changed. I have previously added a custom domain with tld "art" in the old UI and even in the new UI. Now when I changed my configuration and tried to add the custom domain again there is a small alter popping up on the bottom of the page stating "art tld is not supported".

My domain is not a Route 53 domain. When I select Manual configuration I configure subdomains and select a custom ssl certificate (as I did before) but the "Add domain" button is never enabled.

Any clues why the tld "art" is not supported but previously was? Thanks for your help.