@leonhardttobias can you try again to update from the site mentioned before, https://get.adobe.com/flashplayer/about/ ?
flash worked fine before update and works on any other browser.
This doesn't really mean you don't have to update.
Opera blacklists older versions of Flash when they have security issues, so that's why it could work before and not now.
And working on other browsers doesn't mean that much; Safari and Firefox use a different type of Flash plug-in (NPAPI instead of PPAPI) and Chrome comes with a bundled version of Flash instead of using the one installed on your system.
that worked, thank you.
i had to download the deinstall-manager and remove flash from my mac, then i download the new flash version on the website for opera and also the npapi-plug-in version via mac-settings. now it seems that everything is ok.
thank you for your help.