If you want to play offline then go here
You’ll then see this message. Click on it to go into offline mode.
To go back online then go back to the first picture area and click on Go Online.
When the game receives a patch then you’ll need to go online again to update the game to the latest version.
If you’ve started playing then to move your saves from the cloud to local you need to follow the instructions here
and make sure cloud saving is turned off in both the Steam settings that eisprinzessin shows and also in the ingame Options menu.