It seems like yesterday (Jan 12) is the final nail of the Flash coffin when Microsoft decided to shut off the global-wide Flash player and not just a Flash Plugin, which means the NG Player was also affected by this and currently un-playable until farther notice. This tells me that they are seriously wanting to remove the history of flash content. For 20 years worth of content gone to waste.
Lucky, there is another way to play Flash content:
First off is the Flashpoint. I know many of you heard this so I gonna straight to the point. Some say it Windows only but there is support for Mac and Linux. You can pretty much play all the collection of the flash games, Nuff said.
Ruffle is another way of playing Flash games, without using plugins. If you want to play NG Game that currently not converted in Ruffle, use "/format/flash?emulate=flash" at end of the URL of the game you play.
For example: https://www.newgrounds.com/portal/view/592473 then add the /format/flash?emulate=flash in the end.
You can also add Ruffle Add-on in Firefox and Chrome. You can also install it on your website if you have a flash-based website.
Last but not least, their other options as well such as Older Browser (such as Pale Moon), SuperNova plugin, and even VLC, an Media Player. According to this thread, he managed to have an add-on that allows you to play SWF files.
Let me know if you got another suggestion. It shocks how much the company really wants to remove Flash from existion. Yeah, flash player did suck ass due to lag and lack of security but still, the world wide web was covered in Flash for 20 years, and hate to see the history in the waste bin.