In July 2017, Adobe announced that it would stop distributing and updating Flash Player on December 31st, 2020. Web standards like HTML5 provide a viable alternative to Flash content, and organizations that relied on Flash have had three years to replace it. Because Adobe will no longer be addressing security vulnerabilities in Flash with updates, Flash Player now prompts users to uninstall. We strongly recommend doing so—just click the Uninstall button if you get this alert. If you don’t, a Flash Player Install Manager app in your Utilities folder should be able to remove Flash Player as well. Adobe also provides instructions to uninstall manually.
This is also a good time to be reminded that you should never respond to prompts to update Flash Player (specially now that it is discontinued). Most of the time those prompts actually download Malware (Malicious Software) and should be avoided.