Hi Jan!
Android creates a lot of partitions by default. So if you still want Android to function be careful which ones you delete. Also the UEFI seems to have created more than one partition and I think you should keep those as well; otherwise your device might not boot properly. Someone in here definitely knows which ones.
I’m almost in the same situation as you, except I don’t want to keep android, just Windows and reuse the unallocated space from the former Androidpartition(about ~24Gb).
Hopefully someone in here will help us both.