Starting with Chrome 62 the new default is to disable Flash for websites.
Sauce Labs attempted to change this default Chrome setting on its virtual machines; however, there seems to be no programmatic way to enable Flash across all OS images that support Chrome. For this reason, Flash is not enabled on Chrome version 62 and higher on any OS.
If you are running tests that require Flash, you will likely see a pop-up requesting you to allow Flash. If this causes an issue during your test, you will need to add an additional step in your script to select 'Allow' when the pop-up appears. This article from StackOverflow includes a number of examples of how to accomplish this.
Here is Google Chrome's Flash Roadmap: https://www.chromium.org/flash-roadmap