Bit late to the discussion? I have edited the title because it is the Flash Player which will disappear from all browsers, Flash (application) is still very much alive.
Captivate team has prepared since many years for the demise of the Flash Player needed to play SWF which was the only way to publish a Captivate project in the past. Since 3 years, when the EOL was announced I have not published any project to SWF, but always to HTML5.
Captivate is ready for sure, but are the Captivate developers ready? A presentation about the transmission to HTML5 was planned for the eLearning conference which was cancelled due to Covid-19. I would have been one of the presenters. Lot of work lost. Have a look at this survey, which would have been the start of the presentation: