I've recently downloaded Adobe Acrobat Reader DC and Flash player to enable embedded videos in PDFs, however I'm receiving a message that Flash player can no longer be used after Dec 2020. Right now my videos are playing fine but I'm wondering what will be provided as an alternative by 2021? Thanks in advance.
What version of Reader DC exactly?
There is no alternative to Flash after 2020. I'm going to move this question to the Acrobat Reader DC forum as folks on there will be able to better assist with Reader DC questions.
This help doc from Acrobat may be of assistance to your query: https://helpx.adobe.com/in/acrobat/kb/flash-format-support-in-pdf.html
Unless you add flv or swf media it should still work, even without the Flash Player, either with a built-in player or an external one. See: