Hi @Nico5 -
I have had this problem for over a year now.
Windows 10 cannot cope with multiple versions of programs with exactly the same name - I sent a support ticket to Microsoft about it and they revealed there was a change are ‘looking into it’. This was a change that appeared overnight for me in a windows update; apparently something was ‘changed in the way the programme associations are stored’.
No updates for months on this though I’m afraid. That list of open with ‘Cubase, Cubase, Cubase or Cubase’ is just so unhelpful.
I gave up trying to open from project folders and just load the version of cubase I want to use and load manually. I have CB 9, 9.5, 10, 10.5 and 11 on mine as some of the studios and machines I work with can’t upgrade largely due to mac hardware/operating system limitations (built in Apple obsolescence!). 
There are numerous issues with backward/forward compatibility between these versions especially with Variaudio so I need to have all the options available to me!
Please do post back if you get any updates or hear other workarounds. Thanks 