I was able to find a solution on the internet. In my situation I had to remove the old Realtek Bluetooth driver named: RtkBtfilter.sys (C: \ Windows \ System32 \ drivers folder). After deleting the file, the update went without a problem. Here I found a solution...
Hi, For almost 2 years I have Lenovo Legion Y520-15IKBM. I noticed that I have an old version of the system (1803). Windows did not inform me about this. Trying to upgrade to 1903 (or 1909) the problem occurs: The Windows support page has a guide on what to do in this case...