According to the announcement, the latest version of Flash – released on March 23 – fixes a specific bug that was causing problems for some Flash games.
A review of the release notes seems to show that Flash 21.0.0.197 doesn’t contain any security fixes, so this isn’t an urgent update. Unless of course you’re having trouble running Flash games in your browser.
The announcement for 21.0.0.197 contains at least one error: it shows the new PPAPI version of Flash, used in Chrome, Opera, and other Chromium-based browsers, as 21.0.0.286. My own tests, as well as the official release notes, shows that the new PPAPI version is actually 21.0.0.197. I reported the discrepancy to the author.
There is no new version of Flash for Internet Explorer and Edge on Windows 8.x and 10; the latest is Flash 21.0.0.182.
As usual, Chrome will update itself with the new version of Flash.