As OP said, Flash Player won't end-of-life until the end of 2020, however Apple dropped support for it in Safari 14. If you're only browser is Safari and you don't need Flash Player, then go ahead and uninstall it (uninstaller posted at https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html). If you do need Flash Player then it's still supported on Firefox and you can use that on macOS.
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The update notification launches the default browser, if Safari is your default browser, this is why you're being redirected to the EOL faq page. If you do want to continue using Flash Player on Firefox, launch Firefox and navigate to https://get.adobe.com/flashplayer to download the latest version.