Hi martin.0
I am Dave, I will help you with this.
Windows has very limited partitioning capability, when you choose to shrink a partition, when it meets an unmovable file, it will not shrink past that file.
Open the Drive Optimization utility in Windows and defragment that drive fully, then try shrinking the partition again, that usually moves the unmovable files and allows you to shrink a larger space.
If that is not successful, you will need to use a 3rd party partitioning tool like the free version of AOMEI Partition Assistant to shrink that partition