Is there a solution to this?
Gparted gives me
Thanks a lot. Best Regards.
When you installed Ubuntu, you selected to use the whole disk instead of installing it besides your Windows installation. Some people don't see this option for various reasons, so always be careful with what you do and understand what options you select before you proceed.
You are now left with unpartitioned space so you are safe to install Windows. Just boot your pc from your Windows installation media (CD/DVD/USB/Network/...) and use the unpartitioned space as Windows will suggest.
After the installation, you will immediately boot into your Windows and initially be unable to boot Ubuntu because Windows will overwrite your MBR and use its own boatloader that initially, doesn't see Ubuntu. You then have the option to customize the Windows bootloader or re-install GRUB2 as bootloader so you can choose to boot Windows or Ubuntu. There are several threads on stackexchange explaining how to do both.