I published my course to MAC Executable (.app) - Captivate 8. Now my customers who updatet to catalina can't play my course anymore. I tried Captivate 2019 but there is only Flash 11 as the highest option. How can I replace the Flash Player in my .app to a 64-bit Version in my published course?
You should not be trying to publish to any output that uses Flash anymore. Flash will be officially unsupported in a matter of weeks now. Choosing to publish to anything relying on SWF in the output is simply not a viable solution. The advice for some years now has been to migrate all courses to HTML5.
You should also consider updating to a newer version of Captivate, BUT...don't even think about doing that until there is a version of Captivate that is compatible with MacOS Catalina. At this point in time there is no version and even the current version of Captivate 2019 is still waiting for a patch to make it compatible.
Thank you. So the best way to provide my client a standalone version (with no internet connection), is to send them the folder with the HTML5 Output and tell them to click on the index.html file?
I cannot say that I recommend the route you suggest either because HTML5 is not really designed to be run locally from the user's hard drive or from a LAN server. It's designed to be served from a web server or LMS (which is also really a web server).
If you send your client a zipped folder full of HTML5 files published from Captivate, you will likely find that some users might be able to get it to run, but you would also get a lot of complaints and technical issues. Some web browsers won't object to HTML5 content, but others will not let it run due to security restrictions because it's being run locally. The same browsers would have no problem with the same content if it was coming from a web server or LMS.
So, I would suggest you do some experiments and send your specific client some test content and see what happens when they try to run it with their browser of choice. But don't be surprised if you hit roadblocks.