I removed the old disk containing GOG Galaxy and wanted to install it clean again, but failed miserable, as the install does not offer the option tos select where to install it for me.

Is this nprmal , or do i have a wrong setup?

First try to uninstall GOG Galaxy from the Windows Control Panel. It should say the application wasn't found, after which choose to remove it from the Programs list. More details in the GOG GALAXY - The drive or UNC share you selected does not exist or not accessible support article.

Then get the full installer (second link there is for Windows).