I am not finding a search feature, either on the remote or in the TV navigation, that could be used to search available channels.
Also, it appears both Amazon Prime Video and Disney+ are not available in the Channel Store.
When you go to https://www.roku.com/ is the country that shows in the bottom right corner of the page set to Germany? Was the country set to Germany when you first created your Roku account? It's easy to confuse the Roku when the country of the account and the physical country where the Roku is located don't match.
Roku does not offer search features in every country.
There are lists of channels on 3rd party websites with add-links/codes just a quick web search away.
Best practice is to log into roku account on your computer so clicking an add-link takes you direct to right screen in account, then request system update on streamer to make the channel appear on the device.
Roku has just announced their launch in Germany, so everything may not be quite ready:
https://www.roku.com/blog/germany-launch
Those channels should be available:
https://channelstore.roku.com/de-de/details/e093bdb60bb2a48289cd5d3c89b3b140/disney-plus
https://channelstore.roku.com/de-de/details/afbca04cc0e1c93a2ea8f3382b56172c/prime-video
When I click on the links to Disney+ and Amazon Prime Video that you provided, the "Add Channel" button for each of these services is inactive.
So, it appears Disney+ and Amazon Prime Video are not available in Germany.
When you go to https://www.roku.com/ is the country that shows in the bottom right corner of the page set to Germany? Was the country set to Germany when you first created your Roku account? It's easy to confuse the Roku when the country of the account and the physical country where the Roku is located don't match.
Thanks very much, renojim! You identified my problem.
I solved the problem by creating new credentials, making sure these were associated with Roku (Germany).
Now I have access to a whole new world of Roku Channels, including Amazon Prime Video, Disney+ and a host of local German-language TV and video channels.
Happy to help! Thanks for letting us know it worked.