OK…
Because of a number of other problems I have now restored a drive image backup of the Ubuntu partition from August, thus ‘downgrading’ from Ubuntu 22.04 to 20.04… That solved some other problems.
I still use LibreOffice 7.2.6.2 - here on Ubuntu 20.04.
I then restarted LO in Safe Mode and reset my user profile (etc.) to Factory Setting.
Then I tried Create Chart again. But I still cannot move the Chart-dialogue window…
Maybe I should add, that when I have tried to manually update LO by downloading and installing a newer version via the link you also mentioned, it has resulted in additional installations… So I now have 2 or 3 versions of LO - which I find quite annoying! But I have never taken the time to remove the old ones… I guess I was afraid that the versions share some information that would be deleted…
Edit:
I can add, that even the “About LibreOffice” window (Menu: Help → About LibreOffice) cannot be moved.