error message updating to OS 10.15.7 Catalina

Hello everyone,

When trying to upgrade the Mac OS of a late 2013 iMac to Catalina, I get an error message.

At first it wouldnt even download the update and gave an error-message (how Windows, I thought Apple... 'just works'?) Then I did countless things like pressing buttons and pulling plugs while starting up, and it actually worked. The upgrade was was downloaded and installing could commense! YESS! Then, during installation, right after the computer should start up again to install the update, I get a NEW error message (how Windows is that!??), the new error message reads:

An error occurred while preparing the installation. Try running this application again. 

Yeah... ok, did that. Like 4 times, which did nothing.

Does anyone have a clue what to do??

Before installation the computer prompted me that Adobe Application manager and Openoffice.org will not work anymore after the install, so I deleted them (yet I still get a message Adobe application manager will not work anymore)